Thought I would throw in what I have found...
I work with AP/WLC configuration using SNMP directly to wireless controllers -- and then use WCS for support personnel and map tracking. I write scripts that query statistics off each controller, then use PHP/Perl to display the results.
The AIRESPACE-WIRELESS-MIB is the best place to start. Don't know the OID at the moment, but the client info you are looking for is in the bsnMobileStationTable. It lists all the clients (actually looks like the info from the WLC clients page).
If you want more specific statistics (bytes in/out), you can also query the bsnMobileStationStatsTable and bsnMobileStationExtendedStatsTable.
For example, with NetSNMP installed somewhere (and you have the MIBs installed), you can use:
snmpwalk -OQs -v 2c -c snmprwstr -m AIRESPACE-WIRELESS-MIB mywlc bsnMobileStationTable
This command will dump the entire table to stdout. I've written a perl script (fairly straightforward and generic) to take this table and make it into a line-by-line showing of each client.
Hope this helps!
