+1 on the Topaz plugins. Especially "Impression".
+ + for Topaz Impression. I had planned to offer that in my first post, but wasn't sure the OP would want to buy "Topaz Studio", and Impression is not available as a stand alone app now. I have "Studio" so I do have "Impression" but haven't experimented much. It does have a lot of potential though, especially when combined with other apps, plugins, filters etc.(mixed media).
As far as the Photoshop "Oil Paint" filter offering is concerned, one would have to do a significant amount of additional work to make the image seem "natural". On its own it is anything but natural IMO.
Gary