i've been very pleased with my scorpion exo-700. i'm on the second right now, and the first would have lasted another season had it not seen that last physic-defying drop (which included a bounce, spin, slide and a roll).
the vents actually work, and the breath guard does an excellent job of keeping the shield from fogging. the liner is removable if you're into washing them.
the shield has a fairly effective twist-to-remove system. i use plexus and a diaper to clean it, and they're very scratch resistant, even with a thick coat of bugs. the shield also has a nice ratchet mechanism that will hold it up easily at in-town speeds, and allow some airflow at highway speeds if necessary.
on the down side, there's no room for head phones, which is fine for me because i've gotten away from that.
they are fairly inexpensive (~$200) and snell approved.