We've mentioned ways to add a flash drive to the inside of your mouse, but if you'd like a bit more versatility, DIYer Gigawatts shows us how to add a few extra USB ports to your mouse instead.
The general idea is the same as putting flash storage in your mouse: all you need is a USB hub and a mouse with a bit of extra room on the inside. Gigawatts actually cut his USB in half to fit, then soldered the mouse connection onto one of the USB hub's free lines. Then, you can route the Hub's cord out of the mouse and into the computer, providing you with a few extra ports to plug in flash drives, Wi-Fi dongles or small SD card readers. Hit the link for a full guide.