Oddly my most productive place is the train -- especially the shinkansen (I'm in Japan). My next most productive is MacDonald's. It is super weird. However, I think part of the productivity increase is due to it being an unusual place. I don't live anywhere near MacDonald's and I only work there when I visit my mother in law (who lives in a fairly big city). I couldn't possibly afford to travel on the shinkansen all day (although the prospect of travelling for 8 hours and then spending the night in a new city every day is really compelling -- One of these days I'll go up to Akita or somewhere that will take a whole day :-) ).

I like working from home, but I actually hate the fact that I'm basically forced to work from home every day (because I live in the countryside). Quiet is nice, but quiet all the time is a bit hard to bear. At least for me.