Jelly Bean for the Samsung Galaxy SII
There's already a port of Jelly Bean for the Galaxy SII i9100 available from XDA. At the time of writing, many things don't work (including the cell radios, so no phone calls or text messages). Despite that, it does boot up and the touchscreen works fine, so you can feel that Jelly Bean fluidity for yourself, if you so desire.
Link to XDA thread: http://forum.xda-developers.com/showthread.php?t=1739763&page=35
As with any custom ROM there are risks that come with flashing it to your device. Neither I, nor Mobot.net, are responsible for any damage you may cause to your device (including but not limited to data loss and permanent hardware "bricking") by performing any modifications. This information is provided for educational purposes only.