You want quality, reliability and a solid warranty above all else...
Hands down, IBM.

HP/Compaq is another possibility, but I believe that they won't be around anymore in 3 years (or at least in a vastly altered state), so I won't recommend them. Their support is crap as well. First you talk to an Indian tech that may not be able to solve your problem and then redirects you back to an US-based one. 2x transoceanic phone lines = garbled sound.
Dell is a popular option, but they're beginning to outsauce their support as well... More Indian techs that can only follow a script.

As someone else said, you want Centrino (Pentium M). Think of this as a PIII on steroids. A 1.5Ghz is (IIRC) ~as fast as a 2.4Ghz P4.

Just for kicks:
http://www.tadpolecomputer.com/html/products/mobile/
The SPARCle starts at $3k...