I happened upon a blog entry from Marc Robins this am discussing the website mashup findnearby.net. I have been a big fan of mashups of the years and this is probably one of the most useful ones out there.
The site allows you to enter a product you are looking for as well as a zip code and a search radius in miles. It then checks Wal-Mart, craigslist, Amazon and eBay for your product.
I tried it a few times and it seems to work acceptably well. To be better it needs more retailer participation.
Still, this is the type of service that can save your rear when you need a product ASAP and want many options.
As Marc says, when this thing adds click to call functionality it will be even better.