This instructable will show you how to make your own very clean looking 4 port usb NES controller.
I know this has been done before, but I'm posting this to show you how I did it because it ended up much cleaner.
Parts:

1 NES Controller
1 4 Port USB Hub This is the one that I used. It was less than $4.

Tools:

Small Screwdriver
Pliers
Hot glue gun
Hot Knife or Exact-o Knife & Lighter.