e61
Key features:

    * Rich connectivity options - UMTS, Wi-Fi, Bluetooth, USB, Infrared
    * Outstanding battery life
    * 2 megapixel camera
    * Messenger form factor with a full QWERTY keyboard
    * Really large 2.8" TFT display
    * Solid, metallic body
    * Symbian OS 9.1 S60 3rd Edition UI
    * microSD memory card slot

Main disadvantages:

    * Hefty weight
    * No HSDPA support
    * No secondary camera for video calls
    * S60 UI doesn't come with Feature Pack 1

p990i
Main advantages

    * Autofocus 2 megapixel camera with macro mode and LED flash
    * Memory stick Duo/PRO Duo memory card slot (hot-swap)
    * Walkman MP3 player and stereo FM radio with RDS
    * 3G support with video calls, GPRS and HSCSD
    * Wi-Fi 812.11b support
    * Touchpad TFT display with a QVGA (240x320 pixels) resolution
    * Stereo Bluetooth 2.0, Infrared port and USB 2.0 support
    * Conventional keypad on a removable flip along with a QWERTY keyboard
    * Internal 128MB flash memory and 64MB RAM
    * Symbian 9.1 OS with the UIQ 3.0 user interface

Main disadvantages

    * Incompatible with older Symbian UIQ applications
    * No EDGE support
    * Records video with a QVGA 320x240 pixels resolution
    * Display not very legible under direct sun light
    * User interface is not always user-friendly
thanks 2 gsmarena.com