General Cisco SNMP/MIB info can be found here: http://tools.cisco.com/ITDIT/MIBS/servlet/index

The CUCM-specific MIBs are here: ftp://ftp-sj.cisco.com/pub/mibs/supportlists/callmanager/callmanager-supportlist.html

Note also that each hardware platform (for example HP) will also offer additional SNMP MIBS.

As a mature and venerable standard protocol, you will find many resources on the web as far as SNMP programming guides and sample code.