The issue when searching is that sometimes they are called "Call Center", sometimes "Help Desk", sometimes "Customer Support", etc. Also, this blurs into the CRM world as well.
I am NOT endorsing one over another... but here are some products you may want to look at (and there are many more)
http://www.eden.com
http://www.alvea.com/ehtml/help_desk.htm
http://www.groupsoft.com
http://www.gwi.com/websites/default.asp
http://www.relavis.com/default.htm
http://www.crmmadesimple.com/ie.nsf/home
http://www.me4n.com/
http://www.sga.com
www.tjgroup.com
www.proactivecrm.com