Before buying:

Calculate with a generous budget.
Do not think about your current needs. Think about your future ones.
The device should manage all of your electronic daily needs for at least the next three years to come. It is also advisable to foresee your device as a mobile desktop replacement.
The device's usefulness is more important than its appearance which means that it must be practical and robust as opposed to being suitable for taking part in a designer competition.
Sleep the matter over again before buying.

Buying:

Take producers into consideration who have been in the laptop business for a long time and whose main line is computer production and who do not, for example, also produce refrigerators and vacuum cleaners. An advertising flyer which makes big promises at a low price is also not suitable.

The device should offer standard components which are independent of the laptop producer. This means, for instance, avoiding a graphic card from Joe Bloggs or a harddisk which fell off the back of a lorry. Good laptops contain components from IBM, INTEL, 3COM, LUCENT, CISCO etc. Remember that it might be necessary to install a new driver at a later point and this will still be available from a good producer in two years.

The device should be all-in-one which means that the DVD/CD R/W, network card, wireless LAN, analog modem, USB Version 2.x, FireWire, Bluetooth etc. are all built in. With an all-in-one device it is not possible to forget to pack in the wireless card or the bluetooth card or to leave them in the train. All in all devices with built-in components are lighter than those with separate add-ons. They are also much less likely to break down. Apart from that good robust devices do tend to be somewhat heavier than their less robust counterparts.

Floppy drives are no longer absolutely necessary for daily work and are hardly available on the market any more. Should you need one nevertheless, you can hook up an external USB drive. USB floppy drives can also boot DOS. However these days there are other possibilities for doing BIOS upgrades, backups etc.
You should choose a processor of the latest generation. Today (01.01.06) that would be an Intel Centrino Duo Mobile 2.0 GHz processor or faster (but not an Intel Celeron processor).

The harddisk should be 80 GB or more.

Today 1 GB of RAM is customary. Also think about your future needs. 2 GB of RAM (Windows Vista, Photoshop etc.) is definitely better and, what you buy right from the beginning, is much cheaper than a later upgrade.

Graphic cards with at least 64 MB of RAM (not shared) are standard in good devices. Running a large external monitor will then pose no problems whatsoever.
You should pay special attention to your choice of monitor. Many producers have allowed themselves to be persuaded to produce 15" monitors which use 1600 x 1200 pixels as their ideal resolution. Unfortunately this is not ideal for many users because the contents of the screen can hardly be read at this resolution. An ideal resolution of 1024 x 768 pixels or 1400 x 1050 pixels is better for 15" monitors.
The operating system should be Windows XP Professional SP2 (and definitely not Windows XP HOME Edition). XP Professional is only slightly more expensive but is well worth it. Make sure that you get the operating system on a separate CD and not as a 'preload' bundled together with other software. This is also valid for the drivers. (Good producers offer web pages where you can download the latest BIOS, drivers and the like.) You will then find it much easier to configure your own system. Also ask if Linux can be installed easily and whether support is available in any case. Installation of Linux is not possible on all laptops without problems. But if Linux can be installed without a great effort, you can assume that the components are good quality ones.

Conclusion:

There are endless variations you can buy. Don't hesitate to ask here. Questions don't cost anything...