Are there any free standalone presentation tools that shows which keys are pressed on screen?
KeyCastr is not available as build for users without Xcode. Only a community fork (git://github.com/bignerdranch/keycastr.git) is working on OS X 10.7 (Lion) and 10.8 (Mountain Lion).
Mouseposé is commercial.
Related to the Windows 7 Question: http://stackoverflow.com/questions/3529329