CyanogenMod 10, Android 4.1 Jelly Bean ROM built from AOSP is now available for download and its for Galaxy S2 (I9100). In preview form its now available over on XDA Developers by XDA Elite Recognized Developer codeworkx.
CyanogenMod 10 comes with performance and design boost and these enhancements also provide a smoother interface, marter keyboard, advanced voice recognition, improved and actionable notifications menu, etc. this build is early preview build so it will also be packed with bugs and few things might even not work. You can try it out from the above mentioned link. Share your views about it via comments.
Also checkout comparison between CyanogenMod 10 and Jelly Bean.