Well... more information would be nice. Are you 10-13, 13-16, 16-20, 20-30 etc.
Also which genere do you like eg, fantasy, science fiction, Action/Adventure, Mystery, Romance etc etc etc.
Juveline Fantasy is very very good for 10-16ish.
Philip Pullman: His Dark Materials - Pretty good.
J. K. Rowling: Harry Potter - Yes I know either you've already read it, or people have told you how good it is so many times its annoying. But it is really good, and its very addictive. There are 7 books and in each one harry has another adventure. And there are some really good charactors in it, some are very developed.
Holly Black and Tony DiTerlizzi: The Spiderwick series - This is pretty good
Cornelia Funke: The Thief Lord, Inkheart trilogy, Dragon Ride- I've acctully only read the inkheart trilogy, but it was really good and imagantive. It's about someone who can read books out of charactors, and that might sound lame but it's really good
Tamora Pierce: The Song of the Lioness, Circle of Magic, and sequels - I read this when I was really little I think 9, and I really loved it. I don't know if someone older will like it, but I've heard lots of people 13-15ish say it's really good.
Christopher Paolini: Eragon- Can't say I really liked this, but so many other people have I guessed it's worth a mention.
Angie Sage: Septimus Heap - I love this series, I read it when I was 11 and it was awesome. Though I am a bookworm and read at a slightly higher level so don't take that like it's not good for older people.
Erin Hunter : Warriors & Seekers series - The first series is good. The others are a bit overdone.
Narnia - xD I don't care how old you are, you must read this books. I didn't love it like I love some books, but it's basiclly a classic and it's old and awesome. I've read all of the choricles.
Fantasy for older people:
- Lord of the rings: This is a bit hard to read for 11-13 year olds, and I should know because I read it when I was 12 and although I loved it some parts just bored me. He puts lots and lots of details into some stuff and it can get annoying. But it an awesome classic and no reader should not be able to say I have read lord of the rings
-The Pelbar series
Other then that I reccomend shakesphere to older people, Animail farm for older people. Sherlock holmes for teens etc etc etc.
EDIT: Darren Shan and Rangers Apprentice is very good for 10-13 year old