Generally, as the price goes up, the weight goes down, it may be easier to adjust, and it should ventilate/cool better. It may be a trick to find one that fits your head and budget well. I always go for better cooling, being in So Cal where cold means it is 70 degrees outside.
So for mountain biking I chose the Specialized Vice as it has awesome venting. It is CPSC, SNELL B90A, CE and AS/NZS certified (not all helmets are as SNELL is a harder cert to pass) and covers more down the sides, front and back than most helmets. Plus it fit me like a glove and it didn't hurt that the color matched my mountain bike. When I crash it I will buy another. It feels like it can withstand anything, a real solid helmet.
For commuting I just bought a Giro Saros. The fit is not quite as nice as the Specialized, but it feels ok, has good enough venting plus is lighter weight. I had been using the Spec Vice, but forgot it on a drive to the trailhead a few weekends ago as it was hanging off the commuter down in the garage (GRRRR). So I decided to buy a helmet just for the commuter. So far I like it. I chose a nice light white color and will be putting some reflective tape on it.
For road riding, I have a L.A.S Istrion. It is the bomb. No it aint cheap, but it is light, has great venting and adjustability and fits my head very well. The bug screen inside it is a big plus; I've had to take the helmet off and coax a bee out of it a few times so it has been useful to me.
Oh, I have another helmet, the Giro Stylus. Horrible. It does not vent well, but that's not its main fault. The straps are. Where the front straps mount to the inside of the helmet causes them to twist sideways and not lay flat against the side of my head. And they rest right on the little front bump of my ears, the edges rubbing them as I ride. Sucky. So it sits on a shelf as an emergency spare.
Tzvia- rollin' slow...
Specialized Ruby Expert/mens Bontrager Inform RXL
Specialized SWorks Safire/mens Bontrager Inform RL
Giant Anthem-W XT-XTR/mens Bontrager Inform RXL
Fuji Newest 3 commuter/mens Bontrager Inform RL
Novara E.T.A commuter/mens Bontrager Inform RL