Next time you're hunting for icons, buttons or other images to mock up or finish off a design, give Love Vector Free a look. It's a decent collection of free images that scale to whatever size image you're working with.
It's nowhere near the scale of the previously mentioned repository Open Clip Art Library, but Love Vector Free is pitched more toward web designs, buttons and other functional pieces that designers and dabblers might be looking to use or draw from. Got a favourite source for free vector art elsewhere on the web? Pitch in a link in the comments.