My preferred case is the Sena Magnetflipper. Very high quality leather case with optional belt clip. Belt clip is the "Ultra Clip" used by a number of companies and is very solid. The Pearl has never popped off the belt or clip. To remove the Pearl you need to swivel it 90 degrees while pressing the release button so there is no chance of doing this by accident.
The leather flip flips from bottom to top to cover the front of the Pearl. Its magnet holds it in place and also activates the Pearls sleep function. So by setting "auto answer calls when out of holster" and "auto end calls into holster" in the phone options, the Pearl works just like a flip phone, open to answer, close to end. When the flip is open it seems to help direct your voice to the mike with improved sound on the other end and reduced noise pickup.
The case also has a very classy, high quality look. I have a black one for my black Pearl and my wife has a red one for her red Pearl. Both look great.
My only complaint (minor) is that because the flip goes upward, sometimes you can brush against something that opens the flip and, because of gravity, it won't close by itself the way it would if it flipped downward. It's really not much of a problem because a quick flip closes it again and the magnet holds it closed.
Take a look at Sena Cases - Premium Leather Cases : BlackBerry case, Treo case, iPod Touch case, iPhone leather case, and other PDA cases
I have had Sena cases for Palms, Pocket PCs and Blackberries. They were all excellent and outlasted the devices every time.