I've tried Ubuntu on a C series Vaio (long time back) which pretty much died on me a hardware failure at a time within 2 years and right now am using a 15'' HP Probook (4510s) which runs Ubuntu like a dream. The ATI drivers are picked up directly and the only issues that I've run into involve screen brightness screwing up after suspend/resume -- HP seems to be able to support Ubuntu really well.

This laptop didn't cost that much -- around $1000 but the build quality isn't that good -- though the keyboard is excellent (with a numpad).

As a side note -- the best solution seems to be getting a MBP and then running Ubuntu virtually for development and OSX stuff for everything else.