Electric Imp is a wifi client in an SD card form factor. If you want to add wifi to your hardware project, this might be a convenient and inexpensive way to do it (they plan to retail for $25). What’s more is, you configure it by having your phone flash a series of lights at it (using their app), so there’s no need for an interface.
I learned about this because it looks like Lockitron is going to use it for their smartphone doorlock system. Very cool technology, but you are basically exposing your frontdoor to potential hacking. I’m interested to see what security features Lockitron implements.