Any of the NEXT brand seem really good.
I personally have a cheap china one.
640x480 rear and 1080p front.
The front camera is not 1080p and it not even 720p quality.
Rear is amazing quality even in low light.
front is bad in low light.
limited to 16GB card (2 hours recording, then loops)
This unit under £30 on ebay.
I have a new unit i got at xmas but not fitted yet, again dual lens.
1080p front and 800x600 rear
playing around inside the house the front camera is very very good so seems it is true (or very close to) 1080p.
not tried rear yet.
on new unit rear cam can be mounted outside car unlike the old unit.
32GB card limit which will record 16 hours from instruction booklet.
front cam is built into rear view mirror unit. It clips over the mirror with small screen built into right hand side of mirror glass. Good for UK as driver on right, maybe not so good for USA drivers.
Unknown cost as was gift, brand is: StreetWise