Great idea canuckster.
I don't really have many (unless you count tons of scripts for Linux server administration of course..lol) but the most essential program in my world is certainly:
Trillian (Multi Client Chat Application)
http://www.trillian.cc/
I use the pro version but a free version is available which gives you plenty of functionality as well. This allows me to run AIM, MSN, ICQ, Yahoo and IRC all within the same program which helps me tons as I have 10 or so connections constantly for easy communication with contacts using any of these mediums. Second most useful thing about it is that it can be set to automatically log every conversation into a really nice and easy to search history so that you never lose anything mentioned in random chat session.