Is there currently an easy way to root Sony Xperia S with stock ICS 4.0.4 ROM? I'm looking for an easy way, which doesn't need Unlocking bootloader or flashing Roms, just like root solution for SE 2011 devices (one click). It's because I currently use my Xperia S for development purposes and can't afford bricking it! please tell me if there is a solution. Thanks!
There's a guide on Rooting Xperia S ICS and GB over at XDAs. Not having any XPeria device, I cannot verify -- but the comments on the thread confirm it working. It does not even require the bootloader to be unlocked.
Requirements for that method:

Windows
Net framework 3.5 or later

Preparation:

Application Settings: [Unknown sources] checked {Allowed}
Application Settings: Development [USB debugging] checked {Allowed}
Application Settings: Development [Stay awake] checked {Allowed}
Settings -&gt; Display settings [Screen timeout] Set to 30 minutes
If your screen goes off just once then you won’t be able to return to the installation properly. Very important!!
Please think about your battery and try to keep the display brightness to a minimum.
Please use a regular picture for the background. Do not use the default live wallpaper.
Charge the Xperia S’s battery to 80%.
Use the Generic CH (1257-3740) XPERIA S LT26i ROM (6.1.A.0.452).
Can be found here along with the latest FLASTOOL link: XDA FileServer
Net framework 3.5 or later
Gingerbread part 1 and part 2

It also mentions a Root Toolkit.
Installation Process:

Flash Gingerbread firmware wiping data and cache only if you are not on gingerbread
Run Step 1.bat
Install ICE CREAM SANDWICH without wiping anything
Run step 2.bat


To enter CWM recovery you have to tap on sony logo at start few times.
If it does not root properly first time run it again
Thanks to Bin4ry for the files

Alternative: Unlocking the Bootloader
An alternative method involves the SDK, and is described at AndroidPit (German; Google Translate 2 English here). this method, however, involves unlocking the bootloader -- so be aware of Sony's harsh politics when it comes to warranty in this case.