Most hardware is well supported.
If you want good graphics and 3d acceleration, look at laptops with Nvidea cards. Some model Ati cards are working well too.
If you want wireless to work on linux avoid Broadcom like the plague. You can get some of the cards to work but you may have to jump through hoops.
Wireless cards with Ralink, Artheros, and Prism chipsets will work well.
Research the hardware carefully. This could save you alot of heartache later on.
There is no one brand that can be said to be fully linux compatible although some makers are offering linux laptops. Google will help you find those.
There is also a website about linux and laptops too.