Here is another interesting Roman coin I picked up recently on eBay. It is an AE antoninianus of Claudius II Gothicus (268-270 AD) with reverse of VENVS AVG.
I won it in an eBay auction from a seller in Australia where it was listed as "Roman Greek or ? Coin old ancient". Something clicked when I saw it and some quick research revealed how rare it is. It cost me $35.
This is one of only a handful of examples known. This article from "Coin Talk" discusses the coin and its rarity: