A few years ago, I bought a new watch on eBay, for a much lower price than I deserved. There was only one shipping option, the slowest possible, so I waited a full ten days for that package to show up. When it finally did, the return address stared up at me, mocking me: It was an address in the town next to mine, a 10 minute drive at most. I paid $15 and waited ten days when, had I known (or paid attention to) the location, I could have hopped in the car and been wearing my new watch that afternoon.
Flippity would have solved my problem instantly. It's a quick search, a sort of mashup of Google  Maps and eBay, that makes eBay more analogous to Craigslist than a traditional online auction. You enter your search term, your zip code, and your maximum desired seller's distance as a radius, and if need be, the engine even provides you with a drop-down menu so you can refine your search by category and price.
You're given a few different views, the best being a thumbnail view, and all allow you to hover over the map listing to see exactly how far away your wanted purchase is. It's a great little idea, letting you save a bit of money on shipping and narrow your eBay queries with that trendy location-based fun we've been hearing so much about.