OID value: 188.8.131.52.184.108.40.206.1.57.0
This is the 1 minute average CPU utilization for cisco routers. Works on my 7200 router. I think the last .0 will work for other routers in the event that there is more that one CPU add a number.
URL for further info: ftp://ftp.cisco.com/pub/mibs/oid/OLD-CISCO-CPU-MIB.oid
See also the OID Repository website reference for 220.127.116.11.18.104.22.168.1.57.0