Originally Posted by Naigewron
The Roland SPD-S is really the only real option on the market. I would steer clear of the Alesis, it doesn't have nearly as many options.
I use the SPD-S myself, and it's an awesome live tool. I trigger both short samples and whole backing tracks from it, and it performs flawlessly every time.
I've got one as well and it sounds tailor made for what you are looking for.
Couple of things:
1) Immediately buy a Compact Flash card (CF 128, 256 or best - 512mb) as the built in sound storage is not going to hold too much. You can erase a bunch of the sounds and replace them but having the card allows you much more storage and along with a USB CF Card writer/reader, is the best way to get custom sounds into the SPD-S.
2) A common question is: Will the SPD-S store MIDI sequences. The answer is No.
* Manually trigger (by playing the pads) external MIDI sound sources via MIDI Out
* Have internal sounds triggered by MIDI sequencers connected via MIDI In
* Create audio loops using the onboard audio sounds (even imported audio) using something called 'Phrase Maker'. Very cool feature. It also can't generate MIDI Time Code, SMPTE or any other time based external control.
Just things to keep in mind. A great value for the money.