The ThinkPad T Series are my favorite, next is the X Series. The only issues I have had running linux on then is getting fingerprint reader going... I honestly didn't even bother trying.

I have a friend who used to work on the ThinkPad line and she used to go on and on about how their line went above any other she had ever seen - In terms of cleanliness and concerns for static, loose items, hair etc.

When ever I am setting up a new client I invariably suggest ThinkPads, unless, of course, I know they are willing to give Macs a shot.