BrickLink.com has been described as the "Craigslist for Lego" by MAKE in the past, and it's not far from the truth. Lego enthusiasts (many members of Gizmodo, I'm sure) will be sad to heard that the founder of the site has passed away this week. The site has a touching obituary to the young Lego fan. [BrickLink via Brothers-Brick]
This is such a huge loss. Thanks to this man LEGO fans had the perfect one-stop shop for some of the rarest LEGO sets and pieces. Ebay is an infinitesimal speck compared to what this site offers, because you can not only find old sets that are hard to find, you can also part out each individual component of the sets in their database, as well as each individual component of each minifigure that it comes with, and even figure out every single set that any given piece can be found in. On top of that, you can set price parameters for your wanted list, which will notify you by email if parts, sets or minifigures that you want end up listed somewhere for the price range you prefer, and you can have whatever you buy from any store in bricklink be subtracted from your wanted list as you checkout so that you don't get those notices again, if you don't intend to buy another later.
It's really addictive if you're a LEGO collector, and really, you don't have any better options, save for LEGO direct of course.