I have been a fan of UF since I read the first Anita Blake novel, Guilty Pleasures, back when god was a baby and dirt was new. The balance of mystery, fantasy and horror was all I could hope for. Over the years, it has transformed from an outlying subgenre into a major force on the best-seller lists. I have embraced and discarded various series' over the decades, but these are the ones I still read.
1. Dresden Files - Jim Butcher
The current big daddy of UF, a #1 NYT best-seller and cultural phenomenon; it even spawned a (short-lived and mediocre) TV show, as well as a comics series. I've sung it's praises before, and will do so again. Good stuff!
Quick story: My mom knows Jim, so, when I was in the hospital with a collapsed lung, she got him to call and wish me well. He's a great guy. Unfortunately, I can't remember most of the conversation because the Dilaudid kicked in right after I answered the call. Opiates don't mess around, kids.
2. Nightside series - Simon R. Green
Got into this series because of Jim Butcher's blurb on the cover of the first book. This series is both darker and fluffier than the Dresden Files. Basically, there is a side of London where it's always after midnight, magic and mayhem are always on tap, and nothing is what it seems. It's a blast, with enough in-jokes to make any sf/f fanatic smile. Green's Ghost Finder and Secret History novels are also worth a look.
3. Iron Druid Chronicles - Kevin Hearne
On the mythical side of UF, you have a series about a 2,000 year-old Irish Druid who fights gods and vampires. A lot of fun, but there are some iffy gender politics, especially in the first couple of books.
4. Alex Verus series - Benedict Jacka
One of the more political UF series, this deals with the governance of mages in the UK as much as the adventures of Alex and his friends, especially in the later books. A little more dour than some of the other choices here, but still tons of fun.
5. Checquy series - Daniel O'Halloran
The only female-led series on this list (will explain in a bit), and even more political than the Verus books. The Checquy is basically the UK's magical Ministry, and the lead in book one, The Rook, has a leadership role in the administration. She appears in a more supporting role in book two, Stiletto, but the emphasis of that one is diplomacy. Great stuff, but a bit headier than most UF.
About the lack of female-led or, especially, female written UF on this list:
Laurell K. Hamilton may have introduced me to UF (hell, originated it), but I feel the Anita Blake books went off the rails circa Harlequin, to the point where I couldn't even enjoy her other series or revisit the earlier entries. I will always hold the author in high esteem (she also helped my mom early in her writing career), and will recommend her, especially if you want heavy doses of sex in your UF, but it's not my cuppa.
Rachel Caine's Weather Warden series is fun, but I got bored around book 5.
I jumped off the Mercy Thompson bandwagon after book 2; Mercy is a great, tough, amazing woman who, for reasons, always needs rescued. That pissed me off, but if you're willing to give that a bye, they're a lot of fun.
There's my two cents.