I've always considered myself to be well-read mostly because of the hefty amount of classics under my belt, but it wasn't until my Dad started lending me his books that I became widely-read.
My preferred literary genres consisted of Chick-Lit and 19th Century British Literature until my Dad introduced me to two authors I'd never heard of before. Robin Cook healded in a love for scientific thrillers and led to my reading a lot of Michael Crichton as well, and Nelson Demille ushered in an affinity for crime dramas - especially when John Corey was on the case.
These two new genres dumped a ton of boks into my lap that I couldn't put down. I began checking the "coming soon" section on bn.com to see when these guys would publish again - thankfully Robin Cook writes a lot. Eventually I started sending my Dad my copes of Cook and Demille as my collection became more current than his.
After my Dad died, all these books came to me. Now they sit on my bookshelf, slightly out of place among Elinor Lipman and Jennifer Crusie but significantly more important than most of the books in my library. They forever unite me to my Father (I love how books can connect people!) and constantly remind me that steppin gout of one's comfort zone (in anything) can yield something wonderful and new you never knew existed.