Only brand I’d suggest staying away from is Alienware - my experience with them was beyond horrible, both from service and quality standpoints.
Anyway, for a solid desktop-replacement class laptop, good ones start at about $1800. These types of laptops tend to be big and heavy, so make sure to invest in a carrying case too.
CPU - Get a Pentium M or an AMD Turino. AMD is less expensive, and I actually have an AMD laptop right now and have no problems with it so far. 1.8-2GhZ is the midrange of low power chips as far as price goes. Even though you can get 2x or the clock speed out a laptop with a desktop chip don’t do it - they will run very hot (so hot in fact that you may have overheating problems, depending on how well the laptop is constructed and the ambient temperature) and drain your battery fast when you don’t have it plugged in.
RAM - 1 gig, minimum these days. 2 gigs is ideal. You can get away with 512 MB but it’s not going to run well. Most off-the-shelf laptops only ship with 512, if you don’t get a custom one you may need to upgrade it later.
Hard Drive - Depends - you’ll either want the biggest or the smallest. If you have a big media collection look for a laptop with two hard drives, they go all the way up to 200 GB. If you don’t have a lot of space intensive files go with a basic drive, 40 or 60 GB and save some money.
EDIT: Another thing you can look into is getting a big desktop drive, putting in a USB 2.0 enclosure, and using it as an external drive to save money.
Video - Even though you may not be playing a lot of games, save the regret later if you change your mind and look for a video system that does NOT use shared RAM. Dedicated ram onboard the video system will greatly improve performance. If you feel like spending a little extra get a laptop that has a modular video card so it can be upgraded later without a microscope and soldering iron. Also, if you get a laptop with a widescreen (i.e. any aspect ratio other than 4:3 letterbox) make sure the video supports aspect ratio scaling, otherwise if you’re running a resolution with a different asepct ratio than the screen, it’s either going to small (centered in the screen and not scaled) or distorted (scaled to fill the whole screen).
Everything else is pretty the same. I’ve never had any problems with any Dell system I’ve ever owned, only reason I have an HP right now is because Dell won’t ship to an FPO address, and HP makes some good laptops these days too, also getting parts is pretty easy for HP laptops if you’re not under warranty.