Always on the lookout for cool photobooth ideas, I have found a few resources the enterprising photobooth host can use. These sites have everything from theme ideas, to free printable props, to backdrops, to simple inspiration.
Oh Happy Day has (among other things) beautifully designed photobooth props and backdrops. Batteries totally included, as each project typically contains detailed DIY instructions and high-quality build photos. With Valentine's Day coming up, be sure to check out the Sweet Lips props. You are having a booth for V-day aren't you?
Pixilated Photobooth has several nice sets of printable props, from mustaches to wedding props. They also have a lot of nice inspirational shots from booths they've hosted, and be sure to check out their video on how to make photobooth props.
Photojojo has several easy-but-cool DIY photobooth backdrops that can be made for next to nothing. I think the streamer backdrop is a particularly cool way to add a lot of color.