I had thought that the standard unix host template in Cacti would get it, but I looked in the Cacti setup I used last and I only had interface graphs so I may not have actually tried to use that.
First, make sure you have all of the boxes checked on the SNMP screen so the modules are loaded to give the info.
If it helps, we use bsnmpd, and copies of the MIBs can be found here:
http://files.chi.pfsense.org/jimp/BEGEMOT-PF-MIB.txt
http://files.chi.pfsense.org/jimp/BEGEMOT-HOSTRES-MIB.txt