The popular system maintenance utility OnyX has been in beta testing for version 2.1 in past month or two, and while it supported Snow Leopard, many incompatibilities still needed to be addressed by the developer. Yesterday the full 2.1 version of OnyX was released, which addressed a number of issues in the previous beta versions, particularly those that pertain to Snow Leopard.
OnyX can be downloaded for free here (Separate versions are tailored for different OS X releases, so download the one for your system): http://www.titanium.free.fr/pgs2/english/download.html
If you have been using the OnyX beta release, or have been waiting for the final version before using it on Snow Leopard, grab the latest version. I'm a fan of OnyX and use it regularly, especially because it is thorough and free; however, in addition to this program there are a number of other options besides OnyX for running system maintenance routines. Some popular ones include the following: