The Alex Verus series is about as close to Dresden you are going to find without the series actually being about Dresden. Hell, even Butcher is listed as a blurb stating 'Dresden would approve.' What more can you say than that. It has a lot of similarities -- a mage character who grew up trained as a 'dark mage' then ran away where he's not quite a good guy but not a bad guy either.

Alex and Dresden are quite similar in this regard. The difference is the Alex doesn't actually have any traditional powers. Rather, he's a probability mage who's able to look through the near futures and pick the best one. This creates an interesting dynamic the whole way through. And with over 5 books out now, this series has proved itself. Highly entertaining and quite a bit darker than The Dresden Files, I highly recommend it as the next best thing over Dresden. Actually, I would say Alex Verus is better than Dresden as it takes more risks and is a much darker series on the whole.

For another book with a lot of similarities to The Dresden Files, try reading Fated by Benedict Jacka. The premise is pretty interesting and does quite a bit to set itself apart from the rest of the other books in the genre. The protagonist is a mage with only one power -- the ability to see into the future; he lacks the dramatic powers that other mages have. However his prescience allows him to pull off operations with 1 in a million chances of succeeding. Butcher himself recommends this novel as being similar to The Dresden Files on the cover blurb.