Not as easy to find as you might hope since many radio apps include "FM" in their name despite actually using streaming radio, like "Last.FM" it seems to be used as a synonym for "Radio" - also, there are a lot of apps from/for specific radio stations that are
FM broadcasters but the app is streaming...
I've not tried any radio apps other than the pre-installed one, but I found these in the play store...
(this one looks expensive but they offer a 'lite' version, but it's still not a free app
Has a lot of negative reviews but it looks like they have incompatible phones or ICS which fails to run the stock app any way, or they don't realise it is for actual FM signals. There are two reviews from SGP users and they say it is excellent and can't understand the bad reviews.
There's probably others and maybe someone here can recommend one (but as nearly three weeks have passed since you asked, that may not happen
One thing to bear in mind, in case you aren't aware, you will always need to have headphones plugged in as the wire is used as the aerial (you should have the option to use the on-board speakers but the headphones still need to be plugged in)