I like the Georgia Nicholson series by Louise Rennison. It starts with Angus Thongs and Full-Frontal Snogging. I'm reading #8 right now (Love is a Many Trousered Thing).
The Fablehaven series by Brandon Mull, or the Artemis Fowl series by Eoin Colfer. The forst book is also out as a graphic novel, and it captures the tone of the first book very well.
My favorites are:
Vampire Academy series by Richelle Mead
Mortal Instruments series by Cassandra Clare
Wake/Fade books by Lisa McMann
The Hunger Games by Suzanne Collins
Uglies series by Scott Westerfeld
Blue Bloods series by Melissa De La Cruz
Holly Black
Amelia Atwater-Rhodes
Kelley Armstrong
Rachel Caine
Stephenie Meyer
Melissa Marr
P.C. & Kristin Cast
Melissa De La Cruz
Ellen Schreiber
Richelle Mead
Serena Robar
Meg Cabot
Mari Mancusi
Gena Showalter
Katie Maxwell
Christopher Paolini
Cynthia Leitich Smith
Lynne Ewing
L.J. Smith
James Patterson