Menotek Keyboard for Iphone, etc.
I got one of these to use for replying to my e-mails on my Iphone4 when away from home. The phone's keyboard is ok for short messages but when you have a lot of them or long answers, the external keyboard is a blessing. When unrolled it's about 7/8ths the size of a full keyboard. When rolled up it's a little smaller than the Iphone (but about twice as fat). I'm a touch typist and have no trouble using the keyboard although some of the function keys are not in their usual spots.
Two drawbacks are the on/off switch is kind of tiny and flimsy and it requires a USB power source for charging its batteries.
On the positive size it is small, waterproof, pairs easily via bluetooth on the Iphone and is easy to keep clean.
I got mine on Amazon.com.