Ladismith has a few possible crags that can be developed for sport climbing, but at the moment it's mainly this crag George mentioned above (Boontjieskloof), and of course the Outback Crag. A recent forum post discussed all the access arrangements for the Outback crag, please have a look if you're interested.
In Seweweekspoort there are some good spots for bouldering and trad routes, but the poort is under Cape Nature Conservation management and bolting will not be allowed.
The main attraction remains Towerkop. Don't know if you've done it before, but here's the site if you'd like information: http://sites.google.com/site/towerkopinfo
Ladismith is also conveniently situated between Montagu and Oudtshoorn if you're staying a few days and would like to take a daytrip for sport climbing to one of these venues.
George and I have our eyes on another crag or two, and will keep you updated once (public!) access arrangements have been sorted out.