I suggest Scrappies, a sock pattern by Adrienne Fong (Bellybuttonknits on Ravelry) http://www.ravelry.com/patterns/library/scrappie
I have a thing about symmetry, so my first pair were knit from self striping yarn, but this pattern was designed to be used with your sock yarn leftovers. If you scroll through the projects, you'll find lots of fun inspiration.
My second pair, knit from two skeins of Claudia Handpaints and one of Koigu, has been on hold for a few months as I've been slogging through test and Xmas projects. As soon as the last gift is complete, these are the first WIPs I will work on, even though I have projects in more luxurious yarns begging to be knit, simply because the pattern is SO COOL.