Decent screen size (15-16")
High screen resolution
Not too heavy
The rest kind of depends on what I'll be using the laptop for. For example, my I use my current laptop for college and gaming, so it's got a lot of space, RAM, an i7 processor, etc.
I plan on building my next PC from scratch, so all the components will be exactly what I want/need. 😉
If I'm buying a new computer for 400-550+ dollars I will At least 2GB of RAM, a Dual core CPU, 500GB hard drive, decent video card, lots of USB ports, sound card with 5.1 surround plugs for my 5.1 speaker system, and a comfortable keyboard and mouse.