Thinkpad X60 or one of Asus' ultraportables - there's a few models, all of which are a little different in size and weight.
Asus' machines are of excellent quality and feature superior video cards (the A8J looks to be pretty slick), but the Thinkpads are the only laptops that I can say are better still - and while the graphics accellerators are often underwhelming, the tech support is great. On the other hand, with ASUS, you'll likely go through a reseller/configurator - I've had a good experience with JNCS.com.
That said, with a Thinkpad, there's a good chance you'll never need it.
Alternately, if you don't want to pay more than $1,500, a refurbished Thinkpad or possibly a HP/compaq Evo is the only way to go.