Google Maps Mania
Well I suppose this was inevitable. There are now so many Google Maps hacks (err... applications) that someone has created a blog dedicated to following up on them. On that note, if you haven't checked out Google Earth, you really must. I can't wait to see if Virtual Earth delivers something as breathtaking.
Update: To be clear, as someone pointed out, they are no longer officially considered hacks (either way, I'm pretty sure Google wasn't trying to discourage these endeavors before releasing the official API)