DAEMON Tools for Mac
Excellent virtual CD/DVD drive emulator
Although OS X is pretty good at maintaining itself, a helping hand doesn't hurt. Socks is a utility for troubleshooting, maintaining, optimizing, and customizing OS X.
It's suitable for both beginners and experts due to a simple interface that hides an impressive number of customization options. You can fully automate Socks so that you don't have to worry about it while you get on with more important things.
The main function of Socks for many users will be to check and repair damaged volumes and corrupt file permissions, although you can already do this with Disk Utility. It also allows you to tweak Spotlight settings, rebuild volume indexes, clean your system and even optimize internet connection buffers, although this latter feature won't do much to speed up those users on broadband connections.
Socks is also handy for hiding your tracks as it can remove document and web usage history in one step. Finally, Socks can be used to change the look of OS X which is one of the few features that really makes it differ from Disk Utility.
Socks doesn't really match up to tools such as TinkerTool System but its still a very nice to use and comprehensive maintenance utility.