This is the book I have already used
http://www.flipkart.com/physics-scientists-engineers-modern-7th/p/itmdytsfn7kxx2gs?pid=9788131514047
(It is also recommended by R. Shankar on Yale Open Physics Course)
All Chapters have not more than 55 questions which are far easier than University...
University of Maryland Problems of the Week
http://www.physics.umd.edu/lecdem/outreach/QOTW/active/
British Physics Olympiad Books (not recommended by anyone because it is just collection of Previous Problems with Full length Solutions.)
British Physics Olympiads - Book 1: V. Simeonova, N...
My suggestion was based on my university curriculum. I am in 2 semester Mechanical Engineering and recommended text is Purcell with Mary L Boas mathematical Methods while my seniors of 5th Semester are have recommendation of Griffiths with Courant and Hilber Mathematical Physics. and clearly...
Purcell is quite easy than Griffiths and so on Griffiths is easier than Jackson.
Suggestion for OP, do Mary L Boas Mathematical Methods books along with Purcell and don't skip any problems if you are skipping. Purcell is Lower Undergrad book while Griffiths is upper undergrad.
Consider these two articles for How to Prepare for IPhO
http://www.thejakartapost.com/news/2005/11/20/yohanes-surya-physicist-many-dreams.html
Yohanes Surya: Boosting brilliant minds | The Jakarta Post
Yohanes Surya is America Returned Indonesian Physicist who trained Indonesian Physics Team in...