First firmware for Android 4.0.4 ROM for Galaxy S II has got leaked and is available for a download.
Information about the leaked ROM -
Android: 4.0.4
Build date: June 28
PDA: I9100XXLQ5
MODEM: I9100XXLQ5
CSC: I9100OXALQ5
However, there is no any update regarding the changelog or improvements.

Galaxy S II will be getting official Android 4.0.4 update in coming few months.
If you want to install the leaked version then first do a backup as it is full ROM and it requires a full wipe.
Download leaked Android 4.0.4 for Galaxy S II
I adore my Android smartphone! I positively love the HTC Droid Incredible (DInc) that I’ve had a couple years now.While I’m actually over-due for an update, one of the coolest things about an Android phone getting out of warranty is the new-found freedom to enjoy rooting and applying custom ROMS (software versions).