I was looking for some small wireless controllers that I could take anywhere with me, and I found two, the Steelseries free and iMpulse Controller. Here is my quick review.

both controllers are bluetooth, if your computer dosn't support it, just pick up a bluetooth dongle from ebay (I paid a buck)

Steelseries Free
small, little bigger than a credit card
dimensions 4.25 inch x 2.25 inch .75 inch thick
good construction
8 buttons, d-pad and two mini analog sticks
has a rubber coating
light
ios, android, windows support
fits nicely in your hand
battery is ok
really expensive @ $59.99
http://steelseries.com/products/other/steelseries-free-mobile-wireless-controller

iMpulse Controller
really small, little bigger than a 1/64 scale car
dimensions 3 inch x 1.5 inch .5 inch thick
ok construction, you try and take it apart it will break
6 buttons, d-pad, and a mode button
cheap plastic
really light
ios, android, windows support
battery is ok
expensive @ $39.99
http://www.impulsecontroller.com/

In my opinion Ipega's one is quite good too.
http://dx.com/p/ipega-pg-9017-wireless-bluetooth-3-0-controller-for-ipad-iphone-smartphone-android-ios-pc-172963

This is slowly leading to playing '94 on phones. Thanks for sharing!

This is slowly leading to playing '94 on phones. Thanks for sharing!

I've been able to play '94 on my Blackberry Playbook - but not with a controller, just touchscreen buttons.

Yeah, I played on my android phone (I forgot what Genesis emulator I used), but the on-screen buttons were not fun. This bluetooth controller would be perfect!

Wouldn't a cellphone screen be a little too small?

I have the Galaxy S4 by Samsung and with a big screen it is actually pretty easy to see. Hard to play with a touchscreen so a controller would definitely be needed.

You can use a wii remote with your phone if you have one. I can post if interested.