If you haven't played Peggle by now, I don't even know what to say. Play it. It's great. There's even an expansion and a second game out by now -- but those cost money.
The first Peggle is currently free, but there's one catch -- you have to have an Origin account. So long as you sign up for EA's digital distribution service you can log on and grab it. Just be aware that some users are reporting errors, so if it doesn't work just try, try again later in the day.