ive been using craigslist a lot lately. i always thought it'd be useful to have a photo inventory of basically everything in your house. then one could browse the inventory and in one click the item could be put on ebay or craigslist. that old GPS receiver, BAM! one click and its on the auction block.
i think it'd be a fairly decent web2.0 site to do such a thing. using a UPC code or model number, the product details could be auto-populated (i think ebay does this already). Now if you put your location into the system, the site itself could be a craigslist.
craigslist is more powerful than ebay, because shipping is so different. usually the buyer provides front-door service within a few hours, you just have to hand them the item. the 'free' section is even better. people jump on the good stuff and you could leave it on a porch.
i think there is a social networking component that could be tied in as well. borrowing stuff is one idea. if my neighbor's garage is cataloged and some items are visible to my friends and tagged as borrowable, i can browse whats available.