Massive choice out there, if you only want it for Hearing sat-nav ect, plus speaking to a pillion. Then do not spend lots of money as they all work good enough for that. If you want to communicate with other riders then you may need something of a bit higher spec.
I bought a cheap set last year and although it did work between Riders over a fair distance, the control buttons were very fiddly to use and occasionally it would lose signal. I now have the X-Lite Helmet and dedicated system very easy to use and a good bit of kit. Only down side for some is it can only be used with other n-com systems.