VIDEO: GoGoStand for iPhone
The GoGoStand is a plastic folding stand that you can tuck away in your wallet for quick access whenever you need to prop up your phone.
It was designed for all generations of iPhones, but it also works with "many other phones" including the Android G1, Palm Pre and more.
The stand costs $4.99, with free shipping in the US, and is available in clear plastic and smoke coloured plastic.
Thanks to L.Rawlins for the tip.