I think rooting the Samsung Galaxy S2 is the easiest one compared to other android phones from other manufacturers (e.g. HTC, Motorola).
There is not S-Off, S-On things like the HTC phones (e.g. HTC Desire, HTC Sensation XE).
Note: Rooting your Samsung Galaxy S2 voids your warranty!
Rooting the Samsung Galaxy S2 is real simple, you need 2 files :
- ODIN flasher
- An insecure/hacked kernel
For the ODIN flasher, just simply refer to the guide and ODIN file found in this rooting guide for Samsung Galaxy S2.
As for the insecure/hacked kernel, I recommend that you get the speedmod kernel. It is a hassle free and optimized-for-battery-life type of kernel. You can download the latest speedmod kernel for ODIN from the SpeedMod kernel download page.
After rooting, download some useful programs like SetCPU, Titanium Backup and DroidWall.
Have fun with your rooted Samsung Galaxy S2.