Don't take this as an insult but I think Ayn Rand might be a little over your head. I didn't try Atlas Shrugged out until I was a senior in highschool and even then it was very heavy.
Moby Dick is a great one as is Les Miserables (one of my FAVORITE plays BTW). War and Peace is very heavy.. I'd probably leave that one off.
Others you might try are Charles Dickens, the Bronte sisters works (Wuthering Heights, Jane Eyre), Jane Austen, Shakespeare, Sir Walter Scott, Hemingway.
If you want to be ready for books you'll probably have to read in school try:
To Kill a Mockingbird (I think everyone should read this at least once)
Lord of the Flies
The Grapes of Wrath
The Great Gatsby (great book)
Things Fall Apart (another great book.. I kept this one from my Ethics in Lit class)
I could go on and on. I would have listed A Clockwork Orange but it is REALLY heavy and I think a tad mature.
*Be smart.. Do your research!!*