Fever Series

The Fever Series is an Urban Fantasy series by Karen Marie Moning. It stars Mackayla "Mac" Lane, an ordinary young woman who is thrust into a world of magic after the murder of her beloved sister. Determined to bring the killer to justice, Mac soon finds out that not only was her sister not who she thought she was, but neither is Mac herself. The series is comprised of five books, with the fifth and final entry released in January 2011. They are:

Darkfever (Book 1)
Bloodfever (Book 2)
Faefever (Book 3)
Dreamfever (Book 4)
Shadowfever (Book 5)

Tropes used in Fever Series include:

All Girls Want Bad Boys: Mac with Barrons, and Alina with the Lord Master.
Badass Bookworm: Barrons. He owns a bookshop, is named after a publishing company, and is pretty mysterious and badass, what with being immune to shades, Living Shadow and all.
Badass in a Nice Suit: Barrons, Ryodan, and any other person from their club.
Badass Longcoat: Barrons favors these.
Belligerent Sexual Tension: Mac and Barrons.
Blessed with Suck: Mac can see the true faces of all the scary monsters who want to kill off humanity.
Chekhov MIA: Cruce, the Unseelie King, and his concubine.
Compelling Voice: The Druid Voice ability. In Shadowfever, Rowena's sidhe-seer ability is revealed to be mental coercion, which she used to keep a hold on the other sidhe-seers and on Dani to make her kill Alina.
Crossover: The books are the same universe as Moning's Highlander romance novels, with the events of the Highlander books partly to blame for what happened. Says Moning:

As I was mentally forming a polite but firm refusal, in no mood to put my sexy and successful Highlanders on hiatus, she snapped, "Don't even think of telling me 'no'. You're the one who put me here. If not for you and your MacKeltars and Adam and Aoibheal none of this would be happening to me. Now fix it!"

That got my attention. I sat back and listened for a while. And I discovered Mac was right. While I'd been busy in Scotland, chronicling the tales of the MacKeltars, I'd not thought to consider the ramifications of their exploits on a grander scale. Not once had I looked to Ireland, to the original settling place of the seductive and dangerous Fae. Not once had I checked on the Unseelie prison to make sure it was still holding its prisoners. Nor had I cast so much as a brief glance at the walls between the Fae and mortal realms, or I would have seen the danger we were in.

Dead Older Sister: Alina
Dead Person Impersonation: Cruce switched identities with the real V'lane, leaving him to be killed in his place by Aoibheal.
Deal with the Devil: Mac promises to not harm the Grey Lady and her children in return for her healing Dani, and later deals with the Unseelie King to get him to stop Cruce/V'lane.
Defictionalization: "Taking Back the Night", the sidhe-seer anthem that Mac and Dani make up in Dreamfever, appears in BloodRush, the soundtrack to the first four novels.
Downer Ending: Faefever - The walls come down, and Mac is made pri-ya.
Dye or Die: Mac is forced to dye her hair after accidentally running into the Grey Man in order to keep him from tracking her down.
Embarrassing First Name: Dani hates being called Danielle.
The Fair Folk: The old-school, scary kind.
Glamour Failure: One of the many reasons the Unseelie want Mac dead.
Important Haircut: Mac gets one in the first book to disguise herself from the Unseelie.
Last-Name Basis: Barrons and Mac refer to each other as Barrons and Ms. Lane.
Level Up At Intimacy 5: Mac's sexathon with Barrons leaves her stronger than she was before.
Living Shadow: The Shades.
Misaimed Fandom: Pri-ya and Proud. Because you're having uninhibited sex with an impossibly hot guy, it doesn't matter that you were raped, might have died, and had your higher faculties taken away in the process.
Mind Rape: Having "unprotected" sex with a "death-by-sex" faerie prince, if it doesn't kill them, leaves a human addicted (pri-ya) and unable to care for themselves. When Mac is raped by three Unseelie Princes at the end of Faefever, it leaves her a mindless animal.
Not Quite Dead: Barrons.
Normally I Would Be Dead Now: Barrons, his son, and the other eight can't be killed, save for a good K'vrucking. It also turns out that Mac was given a modified version of a faerie elixir of life by Cruce/V'lane when she was raped in the chapel.
The Nudifier: V'laneCruce is a living nudifier; his Fae Prince hormones cause human women to strip off all their clothes in public.
Older Than They Look: Barrons
Public Domain Artifact: The four Hallows, in place of three of the Four Treasures of Ireland.
Rape as Drama: Mac being raped by the Unseelie Princes at the end of Faefever.
Romantic False Lead: Christian and V'lane.
Stalking Is Love: Barrons, whom Mac eventually ends up with, had been watching Mac ever since she first came to Ireland.
Tall, Dark and Snarky: Barrons.
Tome of Eldritch Lore: The Sinsar Dubh.
Took a Level in Badass: Mac gets tougher with every book.
Totally Radical: Dani starts using the word "dude" in Dreamfever, to the point where Mac threatens to start calling her Danielle.
Well-Intentioned Extremist: Ro, to the point where she chews Mac out for not killing someone possessed by a Gripper, tries to kill Mac while she's Priya, and mind-controls Dani into getting Alina killed for associating with the Lord Master.
"What?" Cliffhanger: Dreamfever ends with Mac freaking out over the monster killed turning out to be... someone, later revealed to be Barrons in Shadowfever
Wicked Cultured: Darroc, and arguably V'lane/Cruce.
Woobie, Destroyer of Worlds: After Mac thinks she's killed Barrons, she teams up with the Lord Master in order to later have her revenge, then use the Sinsar Dubh to remake the world.
You Called Me "X" - It Must Be Serious: Barrons only refers to Mac by her first name when she's been brutalized or badly injured — otherwise it's Ms. Lane in a somewhat derisive tone.