Seidio makes some great cases and has some other accessories. On the other hand, some folks have disliked their designs on some phones.
I first picked up a case from them when I got my shell and holster for the Touch Pro, and then got an extended battery and back cover for my Pre from them. Both have been excellent, and a buddy of mine picked up the TP2 cover and holster and loves it. The shape and feel of the shell covers are great and almost look and feel like a part of the phone from my experiences.
http://www.seidioonline.com/