discovered this site today tips4mac.blogspot.com and so far worked back through to Nov 2007 archives.
My favorite tips so far have been about 3 apps.
iRed Lite - get the apple remote working with other apps like VLC. http://www.macupdate.com/info.php/id/23518/ired-lite
Battery Health Monitor - Tells you current capacity of your battery and number of charge cycles you have put it through. http://www.macupdate.com/info.php/id/24141/battery-health-monitor
As a recent convert from Windows (and Linux) I am use to having a start button with access to all applications, which seems to be missing on OS X. So on Leopard i created a stack from the applications folder. However I have grouped a lot of similar applications in folders so clicking on this in the stack just opens the folder in the finder. This program says that it will fix that and I can treat my applications stack just like a windows programs menu. http://www.macupdate.com/info.php/id/26284/hierarchicaldock