You might have a look at Krusell cases then.
I'm thinking something like this (I'm not sure which size exactly is right for the Blackberry (small, medium or large.)
They have a large selection of changable belt clips that work with their cases.
If you don't like the swivel clip you can change it to things like:
Or just used the regular included belt loops.
Of course the only downside to these cases is their universal (not meant for the Blackberry specifically) so they won't have a magnet.