Forbes is a great place for rankings, and since I love rankings, I enjoy popping over to the site on occasion and finding a new list. The Forbes article is here, and the underlying information for the rankings comes from the Environmental Performance Index. (That's a groovy map, by the way.)
Generally, you'd expect richer countries to do better-- they can better afford the economic hit that environmental regulation (like welfare systems) imposes on the economy. To that end, there are some interesting results-- most notably Colombia at #9. Most of Africa does poorly; the danger of a study like this would be to come to the conclusion that Africa is in dire need of further environmental restrictions.