Cmd-Tab switches between applications (as I'm sure everyone knows), but it's less useful on OS X than Ctrl-Tab is on Windows or Linux because it doesn't switch between individual windows in those applications.
Cmd-Tilde (~) was the missing link for me. It switches between windows in the current application. Those two are probably the most important keyboard shortcuts I know on OS X.
Plus, another endorsement for Quicksilver. That's always the first application I install, and I now find it really frustrating to use any computer that doesn't have it installed.
And maybe you should set your Dock to auto-hide, so you're not so tempted to move the mouse over there to monkey with things.