I use a Cycle-Ops Fluid 2 trainer (but not as much as I should). It is absolutely great, period. I would definitely recommend a fluid trainer over a Mag trainer (quieter, more reliable), though they are more expensive. I think the CycleOps 2 lists for about $299, but you can save a lot if you look around (I got mine at a one day sale last year for $199).
Read some reviews at roadbikereview.com. Here's a direct link to the reviews of this model (but read about others too).
CycleOps Fluid 2 Reviews at RoadBikeReview.com
-Stu