Tamil FM: http://www.tamilfms.com is the best site for online tami fm. Its got 80+ tamil online FMs.
In addition to that http://www.TamilFMs.Com has useful links for other informations like Tamil Online Magazines, Tamil MP3s,Tamil Online News,Tamil Recipes, Tamil Searching engines, Tamil E Greetings, etc
http://www.TamilFMs.Com has following FMs in it Aaha Fm,Shyam FM,Tamil Flash FM,NJ Tamil FM,,GokulNath FM, Nila FM,Merina FM,Tamil Aruvi FM,SuperStarz FM,Tamil Voice FM,Num Radio FM ,Geetham Fm,Shakthi Fm,TNS Fm ,Tamil NJoy FM,TSR Live FM,Isai Fm,Thayagam,Radio NRI Fm,Vijay Fans Fm ,Suryan Fm , AR.Rahman Fm,Ilayaraja Fm,Tamil Malargal,Ultimate Fm,Germany Tamil,ETR Germany, THR Raaga,Tamil Christian FM, Canadian Multicultural Fm,London Tamil Fm,IBC Tamil UK,BBC Tamil Osai UK,BBC Seithi Arikkai,Oli Singapore,CTR Osai,SLBC(City Fm), TTO Radio,Mudhal FM
on iPhone, iPad, AppleTV, PC. It's free.