I haven't done much looking for cases with belt clips, so I can't really do much comparing, but this one is really great for the Eris.
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It's a hard rubber and the texture + ridges give it excellent grip. Also, it seems to have the upper hand on a lot of other clips b/c it just slides in and out with some sort of side-pressure-clip. In other words, there isn't a release system that you have to press as you try to pull it out (like the verizon clip that is currently available for the Incredible). It isn't loose enough that it would be jolted out but it slides out perfectly with a little pressure.
Also, the ridged case lies flush with the screen which may be appealing to some ppl.
EDIT: One more thing. They made one for both the Eris and the Incredible, so I am betting one is in the works for the Incredible too.