There are a number of good manufacturers now. Some note-worthies are: shoei, arai, agv, shark, mjc, bell.
You're main considerations may be (in order of importance):
- Budget
- Fit
- Features (e.g. flip chin, sun visor, anti-fog pin-lock, ventilation, removable-washable liners etc).
- Style
I use my bike every day, all weathers, so the helmet choice and clothing is critical for me (pin-lock a must). Most makes have have vents, pin-lock, chin-curtains, breath guards. Fewer are distinguished by sun visors, fewer still by flip up chin guards.
I have owned both Aria and Shoei. I have recently replaced my Shoei xr1100. I had intended to consider a flip-up chin and I really liked the idea of a flip-down internal sun visor as well.
I tried on all the above manufactures and found all comfortable (except MJC which I couldn't get an ideal fit for me personally - but otherwise a nice helmet) and Shark less so.
At the end of the day, irrespective of what anyone thinks about particular a brand or model, I can't stress enough that you simply cannot do better than finding a retailer with a good selection and comparing them yourself.
For example, despite the fact that I arrived at a shop recently with the intention of getting a helmet with all the bells and whistles on, I walked out with a Shoei NXR (called RF-1200 in the states) (which is not a flip-up and has no internal-retractable sun visor either) and even so, was just as expensive as those with. The reason I unexpectedly came away with something that doesn't have either of those features - I discovered that there are always compromises (i.e. weight and bulk). The NXR simply has a fantastic compact shell and light weight that I could not overlook - and having tried them all, this suddenly became the winning factor for me - something I would never have known if I had not been able to do a comprehensive hands-on comparison.
Hope that helps.