Here is a list of some random software I use for the majority of things I deal with:

Zenoss – Open Source Network Monitoring, takes nagios and cacti to another level.  Very customizable, but takes a while to become familiar with the system.  The more I play with Zenoss, I constantly come across new features and advanced functions.

Monitoring Terminal Services sessions:

Monitoring SQL locks:

Monitoring Apache:

Monitoring MySQL:

Dekiwiki – Open source WIKI, with very good media integration and built-in support for Active Directory.  I prefer it over MediaWIKI.

Jing – Free desktop screen capture utility, also creates flash videos on the fly.  Has its own file sharing service screencast.com for sharing your screenshots/videos.  Great for making tutorials.