IGN throw a few names into the hat...
http://uk.ign.com/articles/2013/06/04/who-should-replace-matt-smith-in-doctor-who
Have to saw Ben Whishaw was my immediate thought... but then I thought he'd be a bit too similar.
Which of course also led me to Idris Elba... but he's a bit Hollywood now perhaps.
I would kind of like them to go for a big name though maybe, something a bit different to David Tennant and Matt Smith who both built their names in the role really.
Chris O'Dowd's name interested me which was a surprise, not being a huge fan of stuff I've seen him in, but could be a comedic difference.
Be very interesting to see where the story goes in the Anniversary and Christmas specials and what happens with John Hurts Doctor and how David Tennant comes back... and how it all leads into the next series and the future of The Doctor. If they wanted too they really could make next series very different, like IGN says about previous Doctors could reappear if they wanted.