I found this site last night and really like it. It's faster than Pokevision, better with largescale scanning, and has a better filter. It was with this that I was able to track down a Mr Mime.
Note: I don't know what the red/yellow circles mean. Keep an eye on the filter numbers as you move the map/zoom. I had 2 Mr Mimes in Madrid that were hidden under the red dot until I zoomed enough.
Hmm, well it was coming up with shit in rural Spain for me. That's a shame then, because I found it super useful. My pokedex is now as complete as it can be because of it.