Thinkpad T60 or T61
I love mine, even wrote a little mini-review here: http://kontsevoy.blogspot.com/2007/08/best-notebook-for-linu...
Thinkpads are designed for doing actual work - "UltraNav" unit and the keyboard are to die for. They are #1 reason why I picked ThinkPad over Mac.
My distant 2nd choice would be MBP, and 3rd - Dell Vostro.