Harry Dresden is the only wizard listed in the Chicago yellow pages. As such, he gets some really strange problems thrown at him - either from his private detection agency office, or through consulting work for the Chicago police department.
He lives with a powerful (and very horny) spirit who lives in a skull named Bob, a huge tomcat named Mister, and eventually (several books into the series) a dog named Mouse.
Now Desden must live in the Chicago of an alternate world - not only because our Chicago is not overrun with vampires, werewolves and the like (though 'tis run over with aggressive pan handlers
) - but also because the Chicago in his world has Wal-Marts with extensive garden centers, and a Wrigley Field surrounded by endless asphalt parking lots rather than a charming neighborhood with very little parking. 
Anyway, these little books are fast paced and a whole lot of fun, filled with charming characters such as Harry, Bob, Mouse, and Mister - but also the very dedicated police officer Karrin Murphy, the tabloid reporter Susan Rodriguez, a werewolf named Billy - and a hen pecked knight of God named Michael Carpenter.
Harry must save the city again and again from such things and people as evil mages, fairy wars, and sexual vampires!
So far there are nine books out of a projected twenty (but they are all a lot shorter than the huge books of say, Stephen Erikson or Robert Jordan).
the titles:
Storm Front
Fool Moon
Grave Peril
Summer Knight
Death Masks
Blood Rites
Dead Beat
Proven Guilty
White Night
While the first two books are still fun, I thought that Butcher really started hitting his stride with the third book. And he keeps getting stronger and stronger with each subsequent novel.
Whoa.