A lucky dip of varyingly cheap mail-order board games, aimed at gaming groups; there's a £4 charge if your order's below fifty pounds, but it shouldn't be too hard to get fifty pounds' worth of stuff if we club together.
An online archive of board and card games. You can set a profile and list the games you own, which might be good for seeing who can bring what. (Here's Kevan's.)
An intimidatingly German game-playing engine; download their software onto your computer, and use it to play any of a huge number of German board and card games for free, across the Internet. They've got Settlers of Catan, and Carcassonne, amongst others. (There's an English guide to the basics if your German isn't up to it.)
I've started using this again recently, so would be up for talking people through the basics of it, if anyone wants to collar me online.
A site that lists many of the rules from the 3.5 edition of the game. Useful if you don't have that edition.
Wizards of the Coast have put a load of obsolete source material online, for free.