For a forward only viewing dash cam you can't go far past a Street Guardian SG9665GC V2 or V3.
TheV3 has just been released and can use a 200GB Micro SD Card. Support is 2nd to none, either via "jokiin" on Whirlpool Forum Automotive thread or DashCam Talk Forum on GuardTrak/Street Guardian thread.

I have the SG9665GC V2 with a 128GB Micro SD Card and CPL (Central Polarising Lens) filter on it and it's a great little dashcam, it is discreet when mounted on the Frit (black dots) behind the rear view mirror. Just be aware that the SD card is inserted/removed on the LH side of the cam when it's mounted, I mounted mine on the RH side and too close to the mirror before I realised how hard it was to get the card out.

The cheapest place I have found for the Street Guardian is Strathpine Car Radios in Sydney, they also have an eBay site.

Note: Street Guardian are currently working on a 2Ch DashCam but I have no idea when the release date will be and jokiin will not give any hints either (he is involved in the development of the SG dashcams).