Launchers are used to replace the original GUI - HTC Sense. By using launchers, your default homescreen is replaced with your chosen Launcher.
Some of the famous launchers are such as ADWLauncher / ADWLauncher Ex or LauncherPro / LauncherPro PLUS.

Note: To revert back to stock sense / the other way around for the HOME KEY without uninstalling, go to Settings > Applications > manage applications > Your Launcher / HTC Sense > Clear DEFAULTS. Then press 'home key' and you can select which to be default...

Another tips of enhancing your desktop is by using Icon Packs. Download, create or modify icons that suits to your need and then 'change' your desktop shortcuts to the custom Icon. ADWLauncher EX have this builtin. For LauncherPro/ProPlus user, you may have to download Desktop Virtualiser to make use of it.

Widgets plays an important role in customisation as well. Some simple & nice customisation can be achieved, just with widgets. E.g. Stock Sense UI bases around widgets.

See Post #4 for list of Apps/Widgets

If you want to change your lock screen easily, look for the application "Widget Locker", it have many different themes, or you can even customise yourself!

- Download your desire theme. E.g. Elegant Blues for Sense (THEME)
--- Make sure you download the correct version for your ROM. Read WARNING below
- Copy the .zip to your SDCard
- Boot into recovery and 'Install .zip from SDCard'
- Choose the .zip file
- Confirm flashing
- Reboot and viola

WARNING:

1. Only flash this AFTER you have done the first boot. If you flashed a new ROM, fully boot it for the first time, reboot to recovery and flash this file.
2. Custom Theme usually is a full-package which includes all other changes below - Power Notification, Custom battery 1%, custom font, boot animation & splash screen. If you prefer modifying SOME part of the UI only, avoid themes or choose themes that you like only.
3. After flashing theme, the process is irreversible unless you reflash the ROM on top of it..
4. MAKE SURE THE THEME YOU FLASH IS COMPATIBLE WITH THE CUSTOM ROM BASE. 1.84 based theme WILL NOT work on 1.72 based ROM's, same goes the other way around.
5. As a general rules of thumb, do a NANDROID Backup before flashing ANYTHING. At least you have a backup if you screws up, don't ya?

Some FAQs

Power Notification widget allows you to have quick settings directly, at the notification bar. An example would be as follows:-

- Download your preferred notification widget
- Copy the .zip to your SDCard
- Boot into recovery and 'Install .zip from SDCard'
- Choose the .zip file
- Confirm flashing
- Reboot and viola

Some Collections: [Collection 1] | [Collection 2]

Warning:

1. Only flash this AFTER you have done the first boot. If you flashed a new ROM, fully boot it for the first time, reboot to recovery and flash this file.
2. Some themes will have these included already. You will not have to flash this again unless you want to change the look of it
3. When downloading the Power Notification Widget Themes, MAKE SURE you READ author's note, or specific instructions. READING IS GOOD!
4. After flashing theme, the process is irreversible unless you reflash the ROM on top of it..
5. MAKE SURE THE THEME YOU FLASH IS COMPATIBLE WITH THE CUSTOM ROM BASE. 1.84 based theme WILL NOT work on 1.72 based ROM's, same goes the other way around.
6. As a general rules of thumb, do a NANDROID Backup before flashing ANYTHING. At least you have a backup if you screws up, don't ya?

You can 'cook' a custom battery icons, which includes the battery % currently, or customising notification window's background, etc. Just proceed to UOT Kitchen. You may also want to read on their Guide on How to Cook with UOT Kitchen.

To Cook :-
1. You have to obtain the framework-res.apk for your ROM: Read here
2. After obtaining the framework-res.apk, keep it somewhere to be uploaded later (you'll need it)
3. Proceed to The Kitchen
4. You will be at a summary screen to review, to start modding, click on tab you are interested. e.g. Battery Icons
5. Customise the way you want, do it on other parts too if you are interested.
6. Before you end, click 'File Upload' tab and upload the framework-res.apk. Stick with 'Edify Scripting' and 'Patch9 Autofix'.
7. You may review summary and and click 'Submit work to kitchen' once you're done
8. Wait for kitchen to prepare your 'meal'. Link will be provided once it's done uploading.
9. Proceed to 'Installation Steps' below.

To Install :-
Flash your downloaded file in recovery:

1. reboot into recovery.
2. choose "install zip from sdcard"
3. choose "choose zip from sdcard"
4. locate your file UOT-... .zip in SD
5. confirm "YES - install UOT ... .zip"
6. wait for script to finish
7. reboot phone

Source: UOT Kitchen

WARNING:

1. Only flash UOT Kitchen files AFTER you have done the first boot. If you flashed a new ROM, fully boot it for the first time, reboot to recovery and flash UOT file.
2. As a general rules of thumb, do a NANDROID Backup before flashing ANYTHING. At least you have a backup if you screws up, don't ya?

Method 1: Use Font Changer [Available in Google Market]
- Download 'Font Changer' from the market
- Copy fonts to your SDCard
- Open the app and choose the font

Method 2: Using ADB PC-Suite - by polarzbearz
- Download the ADB PC-Suite here
- Start the PC-Suite.bat
- Press any key, and select your device (In our case for Desire HD: Enter '3' and press 'Enter')
- Manually boot into recovery, or use the option given (choose 'No' when prompted if you are already in Recovery mode or not)
---- However, if it keeps repeating "ADB Server oudated" "killing" and no progress seems to be noted, close the PC-Suite (Your phone will be in recovery already), and restart the PC Suite. This time, choose 'YES' - already in recovery mode.
- Your phone is supposed to get connected at the PC Suite now.
- choose '3' - Font Flasher
- read the instructions (i) if you want - RECOMMENDED!!!
- select 'f' to open the custom font folder, and put your custom fonts in it (renamed into DroidSans.ttf and DroidSans-Bold.ttf)
- now select 'b' to backup your current font - RECOMMENDED!!!
- select 'c' to flash the pasted custom font
- If you want to restore, you can use the option 'r' to restore the previously BACK-UP fonts, ONLY IF YOU DID A BACKUP!!
- basically that's all, remember, follow the instructions stated in the PC Suite!!

Method 1: Manually using Android SDK - by syuki
- You need to install Android SDK (ADB) in your PC.
- Plugin USB cable to your phone.
- Download your prefered boot animation, extract bootanimation.zip and put in c:\android-sdk-windows\tools folder.
- Open CMD (Command Prompt).
- Find the ADB location in your PC, where you installed it. (Usually install in c: drive) --> cd c:\android-sdk-windows\tools
- Enter command in CMD:-

- Done

*** NOTE: This method is tested on ARHD and LeeDroid only. If other ROM that have different storing location for bootanimation, this might not work. Please check before changing!!! You have been warned!! ***

Method 2: Using Root Explorer- by syuki
- Plugin data cable to your phone.
- Download your prefered boot animation, extract the file inside and rename to bootanimation.zip and copy it to root of sdcard.
- Next, unplug data cable from phone.
- From your phone, open Root Explorer.
- Mount to R/W (read/write) first at the top of Root Explorer.
- Copy and paste the bootanimation.zip to /data/local/ (make sure it's read/write).
---- Note: Some others ROM will have their bootanimation.zip stored at /system/media/ instead. Please take note
---- Some XDA members reported that some ROMs will have theirs at /system/customize/resource instead. Please check
- And lastly, reboot your phone.

Method 3: Using ADB PC-Suite - by polarzbearz
Alternatively, you can use ADB PC Suite.
- Download the ADB PC-Suite here
- Start the PC-Suite.bat
- Press any key, and select your device (In our case: Enter '3' and press 'Enter')
- Manually boot into recovery, or use the option given (choose 'No' when prompted if you are already in Recovery mode or not)
---- However, if it keeps repeating "ADB Server oudated" "killing" and no progress seems to be noted, close the PC-Suite (Your phone will be in recovery already), and restart the PC Suite. This time, choose 'YES' - already in recovery mode.
- Your phone is supposed to get connected at the PC Suite now.
- choose '5' - Flashing Tools
- choose '1' - flash custom bootanimation
- read the instructions (i) if you want
- select 'd' and paste your bootanimation.zip in it
- now select '1' to backup your stock bootanimation.zip if you want
- select '2' or '3' depending on which location your ROM stores the bootanimation.zip at
- If you want to restore, you can use the option '4' or '5' to restore the previously BACK-UP bootanimation.zip, ONLY IF YOU DID A BACKUP!!
- basically that's all, remember, follow the instructions stated in the PC Suite!!

Method 1: Manually using Android SDK - by syuki
- WARNING, your phone need to have ENG S-OFF ok.
- You also need to have Android SDK (ADB) for fastboot option.
- Download your preferred Splash screen.
- Extract the file and put in c:\android-sdk-windows\tools folder. (Meaning, put in the same folder as fastboot.exe)
- Plug data cable to your phone.
- Open CMD (Command Prompt).
- Put your phone in Bootloader option --> type in CMD adb reboot bootloader.
- After your phone reboot to bootloader, please type this command:-

- Done

Method 2: Using Android Flasher
- WARNING, your phone need to have ENG S-OFF ok. [/color]
- NOTE: Make sure you have USB debugging enabled. HTC drivers and fastboot/hboot driver must be installed.
- Download Android flasher --> Click me
- Extract it, also prepare an image (which you want to use as the splash) WITH resolution 480x800 with .BMP format, 24bit depth
--- (32bit/16bit WILL NOT work. Any other resolutions WILL NOT work.)
- Run Android Flasher
- Tick 'Splash'
- Press 'Begin'
- Follow the steps/instructions

Some collections of splash screen from XDA-Developers: [Collection 1] | [Collection 2] - credits to forummers @ XDA

A guide on how to create your OWN Splash screen (complicated)