Here is a handy chart for psu requirements.
A 6670 needs a 400w psu.http://www.realhardtechx.com/index_archivos/Page362.htm
I would not buy any of the psu's that allpower is offering.
Stick with good quality units.
Pick a tier 1 or 2 unit from this list:http://www.eggxpert.com/forums/thread/323050.aspx
ATX psu's have standard width and height dimensions; they do differ in length.
Some might be longer than 140mm, so check that if your space is limited.