Two of the most frequent programs that get mentioned in bug/ticket/issue tracking discussions are RT and Bugzilla. Bugzilla is more oriented towards software development and technical personnel, while RT is more business oriented and for non-technical personnel. Recently, though, I am hearing about ORTS pretty often.
OTRS – Open Ticket Request System. It looks like it is very similar to RT with queus, templates, and other stuff. It is written in Perl and was tested on a number of platforms. Check it out if you are in need.