Best free online reference sites of the past 10 years

The Machine-Assisted Reference Section (MARS) of the Reference and User Services Association (RUSA) of American Library Association (ALA) has assembled a list of the best free online reference sites of the past 10 years. 

There's no point singling out the OA winners --they're all OA.  But you'll notice some familiar sites, like the DOAJ (a winner in 2005), and some unfamiliar ones, like the Big Cartoon Database (a winner in 2006). 

MARS picks winners every year and this web site is a compilation of all the winners for the past 10 years.  That explains why some are out of date.  For example, it includes my Guide to Philosophy on the Internet, because it was a winner in 2002, even though I officially (publicly, emphatically) stopped updating it in February 2003.  For just the newest winners, see the list for 2006.