Squidfingers is where I got my background tile for this site (with the color tweaked myself), but a bunch of other cool background tile-related sites have popped up. Tile-a-Day is a great concept and I love the interface to preview new tiles. Tile Machine is an online tilemaker app that lets users store their tiles and features the best submissions.
I usually create and gravitate towards simple interfaces and clean designs, but used sparingly, background tiles seem to add a uniqueness that draws me in (even underwear companies are sporting them!). I suppose that aspect will eventually fade as it did the last time people went background-crazy in 1996 or so.