Depends. I'd say MacBook, but I already have one. Best computer I've ever owned, LOVE IT.
Option two: Asus EEEPC (micro laptop). Perfect for logging/tuning, these things are about $350 and are ultra portable.
http://www.mwave.com/mwave/viewprodu...tebooks+-+Mini
Option three: what kracka said. $500 HP or Compaq special from Best Buy and keep the change.