A friend served crab legs with drawn butter and added a bit of vinegar to the butter. I was a little put off until I had a bite and it's fantastic! The vinegar cuts the richness of the butter and gives it a little boost. I always add it now, whether I'm eating lobster, steamers or crab. And as Blond Logic says, if you want to keep it really simple, a squeeze of lemon or lime juice is good too.