Here’s one I’ve been using a lot: Upcoming. You enter your zip code, and the site returns a list of events happening near you in the next few days and weeks. This includes book clubs, band performances, DJ appearances, book signings, celebrity appearances, art exhibitions, and pretty much any other public event you can think of. I’m amazed at the exhaustive listings; there are over 100 events per day within driving distance of my house alone.
You can also mark if you’re coming or interested, and see how many others have signed up. Most entries list the exact address of the event, with links to Yahoo! Maps and Google Maps for that address. You can even post any event to your iCal, Outlook, Yahoo!, or Google calendar, directly from the event’s page.
And, if you have a Yahoo! account, you can add your own events to Upcoming, direct people to the site, and track RSVPs online with it.
Overall, it’s a remarkably well-designed site that provides a useful service.