Well, I may as well add my 2 pence...
1. Min 4gb ram. If you're running Windows7, that alone will consume 1-1.5GB Ram
2. Personally, I'd stick with Intel over AMD. I haven't had an AMD laptop in several years but if memory serves me correctly, it used to overheat a lot!
3. Dell laptops - had 4 over the last 3 years from work. Good machines, but fan's get very hot if not left on a desk with ventilation.
4. If going for Intel, make sure you get a Sandy Bridge chip and not the older ones (hence you will find some laptops cheaper so be wary of this). Useful link which explains how to identify a Sandy Bridge http://forwardthinking.pcmag.com/chips/282413-do-you-have-a-sandy-bridge-chip-how-to-tell
Nij