I have to say i am a huge fan of Ubuntu. It works so well out of the box and has allot of support for different hardware. Not to mention its so free that they will send you the discs and pay the shipping.

Gentoo is another distro i am a fan of. I love emerge and the speed of the distro. Do a stage 1 install of Gentoo and i will lay money on the table you have never had a faster system running on your machine.