I have had my eye on this since giving it a try at E3 this year.  The ION Drum Rocker Premium Set is expensive at $299.99 list, but if you are really into Rock Band 2 drumming, this is what you have been waiting for.  Amazon has it available now and even at $269.99 (10% off), it is one of their top sellering items.

Check it out:  Amazon - ION Drum Rocker Set

Product Description
Drum Rocker delivers the most realistic drumming experience available to any gamer, regardless of platform. That's because it was built by the engineers at Alesis, one of the largest manufacturers of professional electronic drums in the world. As a result, you get a kit that's designed to take a real beating, with all the positioning flexibility that professional drummers demand. While other drum controllers lock you down to a pre-molded plastic array of pads, Drum Rocker's professional aluminum drum rack lets you position your snare, tom and cymbal pads wherever you want. When you're ready to move from playing Rock Band to playing in a rock band, you can swap the game controller module with one of the professional drum brains made by Alesis, and you're ready to hit the road for real! Drum Rocker's velocity-sensitive drum pads feature a playing surface that is much quieter than other drum controllers. They also feel great ¿ the stick rebound off of the pad is much more natural and consistent than anything else available. The pad housing is made of high-impact plastic, designed to be whacked on stage night after night. No matter how much you punish them, the Drum Rocker drum pads can take it. Complete the experience with up to three cymbals. There's nothing like finishing a monster fill by whacking a crash cymbal. Or crossing over to play your hi-hat with your right hand while you keep the backbeat on the snare with your left. Or keeping time on a ride cymbal during the chorus. Drum Rocker lets you do all that and more, with cymbals that can be placed anywhere around the kit. Drum Rocker comes with two cymbals and mounting hardware out of the box, and a third cymbal is available as an optional accessory. You get to decide how you want to use the two cymbals that come with the kit  set them up as a hi-hat/crash, crash/ride or hi-hat/ride combination, then add the third cymbal to round out the kit. Compatible with ROCKBAND and ROCKBAND 2 for the XBOX360.