I got an email from Robert Broom telling me about iSLCollective. Here's what he says:
The Internet Second Language Collective is a file-swapping community of ESL, FLE, ELE and DAF, Portuguese and Russian teachers sharing free, downloadable language-teaching materials. All printables are originally created by our members, and are in fully editable doc/ppt formats. Launched in September 2009, our resource library now includes over 20000 worksheets, and is growing by the day.
I checked out some of the resources and was impressed by the quality and quantity. And unlike some sites I could mention, you don't have to upload a resource to be able to download one (though you do have to register). The site features a very useful search function which allows you to search by level, student type, grammar focus, skill, etc. Definitely one to bookmark.