Look here to find reviews of machines...
I've got an IBM Thinkpad R32, and except for the modem
which I don't need in the first place it's a very fine machine
to run Linux on. My old TP 770ED worked well, too, in fact
with the old one the modem was working, too ;)
If you decide to go for a Thinkpad I'd suggest getting a model
that uses an ATI Radeon with separate video RAM :}