If you are looking for something to do with leftover sock yarn, consider joining me for the Big Knit and knit little hats for Innocent Drink bottles.
There are 3 patterns on the website and they start by casting on 28 stitches and the hats can be as fancy or plain as you like. A basic knitter could finish a plain hat in an hour, probably less. Finished hats get sent to England and if you want, I will happily bundle all the hats together to save postage. I'm thinking I could whip up a half dozen in an evening. Their goal is to collect 500,000 hats, which will raise 50 pence per hat to help elderly people afford heat during the winter.
I'd like to see a company in the US do something like this too.