The Chronicles of Narnia (series) by CS Lewis
Nope, that's absolutely not cheating! The Chronicles are now bound in one pretty volume. As I see it, if you're going to be stuck on an island for an unknown amount of time and can only have ten books, you may as well make them very long books.
Life of Pi by Yann Martel
In this thought-provoking and fascinating book, the protagonist Pi is adrift on a sort of floating island in the form of a life raft-- a life raft which he shares with Richard Parker, a Bengal tiger.
The Stand by Stephen King
I've never been able to read The Stand. But I really do want to, and being stuck on an island would give me plenty of time to take on this monster of a book.
The Mists of Avalon by Marion Zimmer Bradley
Endless re-readability potential here. At nearly 1,000 pages, Avalon would be another very useful brick of a book to have around for entertainment when entertainment is scarce.
Shogun by James Clavell
Another huge epic book I've never read. But I've heard it's so good.
His Dark Materials (series) by Philip Pullman
Again, not cheating. I could concentrate on finally puzzling out some of the weirder and more mysterious things in The Amber Spyglass if I had this book lying around on the beach.
Harry Potter and the Deathly Hallows by JK Rowling
Of course, I gotta have at least one Harry Potter book. I'm not quite sure why this one immediately came to mind... I guess it's just the most epic, the most satisfying read of the bunch, and an amazing conclusion to the whole wonderful series.
The Lord of the Rings by JRR Tolkien
Another series-in-one-volume, yes. The Lord of the Rings is another series with great re-reading value. I usually re-read it once a year, as a kind of nerdy tradition.
The Pillars of the Earth by Ken Follett
I've only waded through this tome once... would definitely read it again, though. This is an awesome epic about the building of an English cathedral which spans several generations and is a lot more enthralling than it sounds.
War and Peace by Leo Tolstoy
Meh, may as well give it a shot. Most readers seem to either read and enjoy or attempt and fail to read War and Peace at some point in their lives.
And that is El Fin. Leave a link to your Top Ten in the comments and I'll be sure to check out your list!