Keycaster is a jQuery plugin was written to add a keystroke and mouse visualizer to your browser window. It is similar to keycastr for the mac, except this only works inside the browser window.
This plugin is still in the alpha stage because it doesn't show all shifted keys properly and some key symbols do not work in all browsers (written mainly to work in Firefox). Also I plan on making this script work as a bookmarklet so you can just click on a link to activate it.
Update: You can now add this script to any page using this bookmarklet - Keycaster - just drag it into your browser bookmarks and click on it whenever you need to visualize your mouse or keyboard actions.