Moby Dick. That book seriously ruined literature for me... I really don't think that there is, or will be, another book that is so meticulously crafted. Moby Dick is the most influential, informative and creative tome of awesome that I have ever read.
Cormac McCarthy's The Road is also a very easy and very quick read that I have read several times and have only owned the book for two years. It's definitely the most emotional book I have read.
Huck Finn. It is the only book that I have finished and then immediately started to read again.
I consistently read a lot of H.P. Lovecraft, he mostly writes short stories, but I read through one of his collections multiple times a year.
I also read The Fellowship of the Ring all the time.
And The Old Man and The Sea. It has become tradition for me on the first warm, dry, sunny day of spring to go sit in the woods and read it from cover to cover.