Generally DOT is ok, snell if you want to do track riding (depending on the track).
As for places, too many to list! Depending on location I have had luck with Royal Distributing and GP bikes (I'm out in whitby) and I will never buy a helmet online! Some guys will go to a store and size them etc and then order online but I figure if a guy (or gal) is willing to spend some time with me ensuring my questions are answered and I am comfortable and confident with my choice then the least I can do is give them my business (plus I hate online shopping!)
Dennis