I haven't heard Jim Butcher recommended. The Harry Dresden novels are excellent. The first one or two are 'okay', and then they just keep getting better and better with each one from there. Be sure to read them in the order they were published, as the characters and storylines progress with each book.
Another great author who, unfortunately, never published much (due to having to make a living), is Daniel Keyes Moran. He has made his books freely downloaded from:
http://www.immunityinc.com/resources-dkm.shtml
Particularly (and again, read IN order): Emerald Eyes, The Long Run, and The Last Dancer.
And, of course, if you've never read Lois McMaster Bujold's Vorkosigan saga, WHERE HAVE YOU BEEN???