You have the 233B, and are just looking for micro-ballhead recommendations?
I have used a Giottos MH-1004 on mine, it's decent. It holds a 600EX-RT, although if you grab the flash and try to move it, you can overcome the clamped ballhead.
I recently purchased a pair of Novoflex Neiger 19 ballheads, to use on light stands with small modifiers (grids/snoots/gels). Unlike the micro Giottos which has only a 1/4"-20 stud, the Novoflex ballhead comes with a cold shoe (with a 1/4"-20 stud under it). The Novoflex holds more robustly than the Giottos.
The Novoflex has a slightly larger base diameter than the Giottos. With the eccentric position of the reversible spigot on the top of the 233B, the Novoflex overhangs a bit (~3mm max), whereas the Giottos is almost flush (maybe ~0.5mm overhang).
I can take some pics later, if you like...