I knew iStockPhoto gives away a free (high-res) image each week, but I was completely unaware that they also give away a free vector each month (and video, if you're into that). I'm not sure how long this has been going on, but I stumbled onto the vector freebie in one of the latest iStock email newsletters. Oh, and I should probably mention that you need to create an account in order to download all the free stuff. Thanks iStock!
Here's a previous free vector from iStock
If you forget to bookmark the page with the free files, or miss a month, the previous free downloads are located below the larger image.