[keanex]

Apparently the M2=GR03? According to this thread they are. I've never heard the M2, but I've heard they're a bit bassy, but they seem to be better built than the Betas. The M4 is also coming out soon which I'll have next week I believe to review/compare if you want to wait. If you're not too worried about build quality though I don't think it's possible to beat the Brainwavz Beta for a sound quality to price ratio.

 

[yipcanjo]

The Brainwavz M2 (aka ViSang R03) are great ~$50 IEMs.  Nice low-end, decent clarity, and all-around nice sound.  I've had issues with two pairs of them now, unfortunately, though both at the hands of my son.
 
Another option would be the MEElectronics A151-BK, which has good reviews on Amazon *and* here on Head-Fi.  NewEgg has these for $59.99 right now + a $20 off code (EMCJKKF89).
 
Hope that helps.

 

[Varley]

The M2's are brilliant but I sold them once I received my Betas, I just ended up using the betas a lot more, not much in sound though, the M2's were slightly more forward and detailed, but the Betas impressed me more