FM radio for Xperia arc S with CyanogenMod? How do I listen to radio on an Xperia arc S? 

I use CyanogenMod (version 7.2.0), which does not include an FM radio app.
The programming support for the FM radio service that is in place within CyanogenMod 7.2, is probably not compatible with the chipset used in Xperia arc S. Hence the omission of the FM radio, it supports only Broadcom BCM4325, Silicon Industry 4708 and 4709, and lastly Texas Instrument WL1271.

Looking at pdadb.net for the specification of the handset - the chipset is not documented, so it's proprietary in which case CyanogenMod 7.2 has no support for it, hence the omission of the FM radio.

The best bet would be to find the original stock ROM dump of that here on XDA, extract the radio app (could be called FMRadio.apk) from it and push that across to your handset.

Edit: As confirmed by the OP, there are dead links galore on XDA. However, I found another linky that may do it (Post #72). (That's err... ICS ROM dump... it might be worth a try.)

Edit 2: Here's the radio stuff, you need to install it in this fashion.

After unzipping the archive, there are two files, FmRxService.apk, and Radio.apk. Plug in the cable to the handset and enter the commands,

adb install FmRxService.apk
adb install Radio.apk


The radio should now appear in your applications drawer, fingers crossed and good luck. There is no guarantee it will work either...