Raphnet created a 16 button USB game controller. no analog support but it is still a cool project. Great as an alternative to a key encoder or as opposed to hacking a joystick.
I have used most of this guy's boards before and they are great. My current cab has 6 of his circuit boards and they all work well together. I used ipac for last project. if might consider this on next build.
http://www.raphnet.net/electronique/usb_game16/index_en.phpnot sure if it is for sale yet but source code is there with all info for you to build and i am sure it will be for sale later.