I highly recommend the HubBub mirror. The mirror is large with good optical quality, it attached easily to my helmet and only took a few tweaks to get it adjusted perfectly. I don't remember what it cost anymore but I can't imagine riding without it so I think it was worth the price! I bought it a few months ago after trying a Blackburn helmet mount mirror that was too small, too far outside my field of vision, and vibrated too much on its plastic beam. I would have bought a Chuck Harris mirror but they are hard to find (which is why HubBub designed a similar mirror).

I used the Take-a-Look mirror a few years ago and liked it as well but I like to take my sunglasses off from time to time and it is nice to still have the mirror available.