My GF and I are both running Eighth Inch cogs. The black coating that is supposedly supposed to prevent rust or something actually doesn't do anything, because it comes off as your cog wears. Still good cogs, though, and I would recommend them.
I just ordered a cog from Scrod's site, as it was only $18 shipped, which is still $6.50 less than the Eighth Inch cogs on eBay. I trust they will perform fine as well.