No lasher in the Complete Warrior. In fact, there are no "weapon master" classes really, unless you count the order of the bow initiate, and that one has a slightly different schtick. The closest you might get is the kensai, but ghod only knows what schtick that PrC is supposed to have.
It seems that they're taking a different tack on weapon masters in general. Rather than specialist classes like the lasher and master of chains, there are several weapon style feats that give you various stunt-type abilities. There's also an exotic weapon master PrC, but it's really just a way to get more weapon style feats.
I'm not sure which approach I prefer. The feats approach is a lot easier and more convenient; it can be tough thinking up cool and interesting abilities to fill out 10 levels of PrC advancement. OTOH, a PrC lets you attach an identifying label to a character, and has a certain amount of cachet to it. It means something to a lot of people to be able to write "lasher" or "master of chains" on a character sheet. Feats have a rather impersonal feel by comparison, regardless of their mechanical features.
So I guess I'm looking at the 3.0 Lasher. I agree with hong that there's something to being able to write "lasher" on your character sheet. 
