Futaba
http://www.2chan.net/script/
Futallaby (up to 040103)
http://www.1chan.net/futallaby/
Wakaba
http://wakaba.c3.cx/
moeren
http://moepic.dip.jp/gazo/script/index.php
siokara
(seems to be still in heavy development.
couldn't find a link to an available
version of the script)
http://siokara.ath.cx
Swetnote
(couldn't find a link to an available
version to the script, it's probably
only for people who register or
perhaps even a pay-product?)
http://www.sweetnote.com/
The gazo-ch concept is interesting, since it places more emphasis on threads, and less on individual images. It seems good for the kind of board where you'd have pictures sorted by category. Apparently this seems to be mostly porn sites.
It is somewhat tempting to write, say, another look for wakaba that would emulate this, but this would probably just be feature bloat.