If you're a teen, try The Hunger Games by Suzanne Collins. Give it about 50-75 pages to grab you. Divergent by Veronica Roth is also excellent.
If you're an adult, try The Buffalo Soldiers by Chris Bohjalian. It's kind of a family drama sort of story.
If you're more into something creepy, try The Ruins or A Simple Plan by Scott Smith.
Finding a book that you can't put down depends on your age and what type of books you've enjoyed in the past. If you're not much of a reader, list some of your favorite movies or TV shows. Most Y!A users can pick a good book with just a little extra information.
Anything by Stephen king or JK Rowling, or read the Twilight series/saga
EDIT: i just started reading Twilight 3 days ago because potter is over & my extremely tiny library doesn't have many books. im on the last chapter now, its DEFINITELY no harry potter, but its still really good.
read the Hunger Games by Suzanne Collins, i read the first one in 5 hours straight and cried in the last one, they make you laugh and cry at the same time, and keep you hooked until the last page! the first one is becoming a film on the 23rd march 2012, with the 2nd book being made into a film shortly after. i promise you that you will not regret reading this trilogy! of course it is your chose, because i don't know what books you like, but i have never regretted reading them, also the City of Bones and its series are great, and you have to read Robert Muchamore's series CHERUB - best books ever!