Philly knows. I've gone through this same . . . type of search. It was also a "learning experience," as I'd usually insisted on "brand-new-under-warranty" for motherboard purchases.
There are a lot of Z68 and Z77 boards available as "RMA/refurbished" and [just plain] "Used" available through E-Bay and Amazon.
There are also boards that could inspire more confidence in potential buyers, sold in the store-front of operations that advertise their services as "corporate IT asset" handlers -- they buy "corporate turnover" and have the facilities to do "serious" repairs and replacements:
www.ascendtech.com
That's the face they present to the potential corporate customers. The link to their "store" is for anyone looking for surplus or refurbished products to buy.
I see a few Z68 ASUS boards, at least one Z77 ASUS board and a Gigabyte board in addition to the ECS and other offerings.
See what you can get at EBay and other sources. You can also find some pretty good deals through Ascendtech, and they seem to know "what they're doin'."
And you could get a P67 board. But why take the step backwards? some of the Z68 boards are ready-compatible with Gen3 processors. As are the Z77's.