Summer Knight (Dresden Files 4) by Jim Butcher. The Dresden Files novels, which were already fairly good, take a big step to terrific with this complicated novel about Dresden investigating the murder of the Knight of the Summer Court of the Faerie, and then getting involved in a war between courts of Winter Faerie and Summer Faerie.
The whole Celtic faerie thing with the Seelie and Unseelie courts has been so overdone, but Butcher manages to make it fresh AND believable in the contemporary Chicago setting: i.e., the Unseelie/Winter court lurks in the subterranean tunnels beneath Chicago, and the Summer/Seelie Court dwells in gardens atop sky-scrapers.
This novel feels epic in several places, notably when Dresden travels between dimensions and joins the war. Not easy to sustain an epic feeling in a first-person comedy novel. Fast-moving, suspenseful, thrilling. You can find it on Amazon through this link: