The Linux Laptop Sites are a great resource for finding out what works and what doesn't on a particular model of laptop.
http://www.linux-on-laptops.com/
http://tuxmobil.org/mylaptops.html
http://www.linlap.com/
Look at what laptops manufacturers are selling with Linux.. If a manufacturer is selling or certifying a particular model, odds are it will work well with whatever distribution of Linux you wish to install on it.
Dell Linux Laptops...