The folks at diyphotography.net have a good post with seven easy DIY projects that will help beef up your photo studio. Beauty dish, dual speedlight mount, ring flash, softbox, snoot, suction cup mounts (very clever), and a PVC light stand. All of them are useful tools.
I like the beauty dish project as an easy, cheap way to get that softbox look. These things can range in price from the $50 range to a well over $200. The version described here will cost next to nothing, especially if you source the supplies at the local thrift store. Here’s a good example of what a beauty dish does for lighting:
(no, that’s not me – it’s just an example I found online)