What is the proper ring finger for a single man?

Well just about any finger you want apart from the left ring finger.

Though wearing one on the index is a bit strange and the little finger is a bit camp.

But that's just my opinion. Personally I think men should only wear 2 rings at the most,(including wedding bands.) Women who wear loads of rings look a quite weird as well. The right ring finger is always a safe bet, middle on either right or left and the right hand thumb can be pulled off by some however some also associate that with homosexuality.

But hey, it's up to you.

I have a larger diamond ring on my left middle finger, and another ring on my right "wedding" finger. Looks good =)