I think it's found under Romance (but doesn't belong there, IMHO) but the Fever series by Karen Marie Moning is so good! A friend introduced me to it several months ago and I've read it several times. My only complaint about the series is that the final book is so far away

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Several of the books in the series have been NY Times bestsellers, and the current release debuted at #3. It's down to #12 now, but as I understand that's because it is totally sold out right now.
The reading order is:
Darkfever
Bloodfever
Faefever
Dreamfever
Shadowfever (not sure when it'll be released)
KMM has another series called the Highlander series. It's straight up romance with a little fantasy thrown in. It's not "related" to the fever series, but if you read it first you'll have a better understanding of some of the events and characters in the Fever series.
I'm currently reading the Dark Hunter series by Sherrilyn Kenyon. I'm not sure how I feel about it yet. It's too romancey for me so far. I know it's pretty popular, though.