I got tired of breaking off the fiddly grippers on Josef Prusa's Igus-bushing-compatible X-carriage, so I beefed up the bushing holders to be simple holes more suitable for press-fit Igus bushings (which you can get at techpaladin.com). Now there's no way you'll break them, and they hold the bushings more securely, too. If you find the holes too small to fit your bushings, you may need to ream them a bit.
You can get the belt clamps from https://github.com/prusajr/PrusaMendel/tree/master/metric-prusa
I've uploaded the .scad files that I modified to make these parts. They may have additional dependencies, but you should be able to grab those from Josef Prusa's github at https://github.com/prusajr/PrusaMendel/tree/master/source
If you use Igus bushings, you may be interested in my Igus bushing-compatible Y-carriage bushing holders:
http://www.thingiverse.com/thing:14593
…And X-ends:
http://www.thingiverse.com/thing:14494
Update 01/15/11: changed extruder mounting holes to fit M4 screws
Pointedstick
