This is Jag's "Yet another extrude filament drive", modified to work with a 8mm bearing on the idler arm. (http://www.thingiverse.com/thing:7113)
Use this if you only have one 606 bearing, have access to 8mm bearings, and are in a pinch.
8mm bearings are commonly available on longboards and skateboards. (ID 8mm, OD 22mm, width 7mm).
Nov 20, 2012 update:
If you're having issues with breakage and need stronger parts,
MarcusWolschon has created this buffed-up version: http://www.thingiverse.com/thing:35092
Print, clean up, (may need to clean holes with a drill).
Assemble via Jag's instructions (http://www.thingiverse.com/thing:7113), using the same parts, except substituting a 7mm hex head (or 6mm, if you can't find one with small enough hex heads) screw for the idler arm axle.
Yes, support is also included already for the idler arm.