There are quite a few out there, take your pick! Prices do vary, but they can provide you with a wide range of custom tunes for various vehicles. Most require PCM swaps, but some offer a handheld solution, such as Wait4Me. If you want any more info, do a search, or visit their website. I do suggest calling them rather than e-mail though.
Note: Wester's also has many other local dealers.
If you would rather tune it yourself, check out these 2. Just keep in mind that there is a LOT to learn if you're interested.