Many cheap retro controllers look the part, but fall down when it comes down to build quality. Thankfully the iBuffalo classic USB gamepad doesn't succumb to these issues. It feels every bit as good as an original Super Nintendo pad does.
The good thing is it will run on just about anything: Windows, Macs, Raspberry Pis and so on. Everything I've tested this on worked just fine, without the need of any drivers, which is nice. I've found the controller great not only for use with emulators, but with modern games like Shovel Knight too.
The only thing I can fault is not being able to re-map the turbo and clear buttons -- it'd be great to use them for save-state purposes.
On Amazon, the iBuffolo seems to go for anything between $US9.45 ($13) to $US18.06 ($24) depending on the seller. Australians may be able to pick it up on eBay for around $25 to $35.