Well, I'm going to go in a little bit of a different direction then everyone else..
1 - HANDS DOWN - The Vampire Series by Anne Rice. You honest just don't get any better then that. LOVE LOVE LOVE!!!
2 - I would have to go with the Odd Thomas series by Dean Koontz. I freaking love it, and Odd is such a darn lovable guy.
3 - The Camel Club / King series by David Baldacci. He is such an intense writer that just grabs you and makes you hang on. Sort of like Robert Ludlum's The Bourne Identity.
I can't really number these but I LOVE the Alex Delaware novels by Johnathan Kellerman, and Dave Robicheaux by James Lee Burke, and Myron Bolitar by Harlan Coben.
Any of those can be interchanged as long as Anne Rice stays as number one!
One a more fantasy of sort, although it's not really my thing, I did read the first two books of the Mortal Instrument Series (City of Ashes and City of Bones, I believe) and they were actually really good!