[foxylad]

Consider Electric Imp too - very small, very cheap, wifi built in, and the web connectivity is handled for you so you don't need to set up/secure/manage an http server.

I've got one that will control my electric desk from my phone, one day soon.

[Revex]

The Imp seems cool, but it's price point (when combined with the breakout board) is higher than a Raspberry Pi and Usb Wifi dongle. Not only is the price higher, the hardware isn't nearly as capable.