Taken from a Q&A off Cisco's site. FYI:
Q. How many APs can Cisco WLCs support?
A. The number of APs supported per WLC depends on the model number:
2106—A standalone WLC that supports up to 6 APs with 8 Fast Ethernet interfaces.
4402—A standalone WLC that supports either 12, 25, or 50 APs.
4404—A standalone WLC that supports 100 APs.
5500—A standalone WLC that supports 12, 25, 50,100, or 250 access points for business-critical wireless services at locations of all sizes.
WLCM—A WLC module that is specifically designed for Cisco's Integrated Service Router (ISR) series. It's currently available in a 6, 8 or 12 AP version.
WS-C3750G—A WLC that supports either 25 or 50 APs that comes integrated with the Catalyst 3750 switch. The WLC's backplane connections appear as 2-Gig Ethernet ports that can be configured separately as dot1q trunks to provide connection into the 3750. Or the Gig ports can be link aggregated to provide a single EtherChannel connection to the 3750. Because the WLC is integrated directly, it has access to all of the advanced routing and switching features available in the 3750 stackable switch. This WLC is ideal for medium-sized offices or buildings. The `50 AP' version can scale up to 200 APs when four 3750s are stacked together as a virtual switch.
WiSM—A WLC module that is designed specifically for Cisco's Catalyst 6500 switch series. It supports up to 300 APs per module. Depending on the 6500 platform, multiple WISMs can be installed to offer significant scaling capabilities. The WiSM appears as a single aggregated link interface on the 6500 that can be configured as a dot1 trunk to provide connection into the 6500 backplane. This module is ideal for large buildings or campuses.