OS X does a pretty good job of maintaining itself due to its Unix core, but there are times when you'd like to run some of its self maintenance tasks manually, and that's where IceClean comes in.
Just using the built-in Unix System Tasks that underlay OS X, you can clean out system caches for both the user and root, delete temporary files and remove log files all from IceClean's menu-orientated UI. If you feel your Safari is a trudging a little, there's even an option for a Deep Safari Cleanup, which should go someway to helping speed up your experience.
IceClean isn't all about cleaning though, it features a whole host of maintenance options including the usual verification and repair of your system disk, disk permissions and .plist files, as well as database optimizations including Launch Services. You can run the whole lot with one command or even schedule the maintenance tasks to be run daily, weekly or monthly at a time to suit you.
IceClean can also poll the system for all sorts of information like system, disk and kernel information. Whois and network lookup tools are there too for network diagnostics. You can also force a Time Machine backup, kill Dashboard, speed up Spotlight indexing, force empty the Trash, modify screenshot settings and perform many other small tasks using the Utilities menu.
IceClean is a one stop shop for most of your maintenance needs. It's not as user friendly as other options like Onyx, but for the sheer utility built into one app, IceClean is worth the free download.