As some have said, fit is very important - try it on! Some helmets fit oblong heads better (Simpson, Arai), some fit round heads better (Bell and, from a brief impression, HJC).
For an inexpensive Snell SA helmet, check out HJC's (
http://www.hjc-motorsports.com/) AR10. A co-worker just got an Si12, which isn't cheap, but it's light and seems well-made. The rubberized coating on the black version is really cool, too.
ScheerSpeed, I can't quite tell...is that a Pro Formula Mazda in your avatar?
Richard