On a whim, I bought an Incipio horizontal case the other day and have to say I'm impressed so far. It's not wide enough to use the Seidio extended battery so I'm now alternating batteries. I use the regular battery on weekends when I'm not at work and the extended (680 carried in pocket) during the week.

Back to the case.... it has two SD card slots inside and the belt clip is really firm. Stitching looks solid and the magnetic flap holds the phone securely.