Oh where to start (We're packrats when it comes to books in our family)
One of the oldest books I have is a 1950's Edition of 20,000 League's under the sea by Jules Vern that belonged to my Grandfather. I used to love to curl up with it when we went to visit him, and he ended up just giving it to me one year. While it's yellowed and worn now, after so many years, just picking it brings back memories of Warm summer days, of curling up with a book on the verdana, with a jug full of icy cold squash. Good Memories
I've also got a good collection of Earl Stanley Gardner's work, ones which my mom grew up reading, and in turn so did we during our holidays.
Of books which we were give or bought when we were younger, We still have most of our Enid Bylton collection, wit most of the singles and smaller series, and large parts of the Famous Five, Secret Seven, etc as well.
We still also have our Nancy Drew's and Hardy Boys, which our younger cousins now enjoy when they come over. While formulaic, they were a lot of fun, especially when you read the crossover Supermystery's when they got together.
Also Have a ton of my old comics, including my Astrix's and Tintin's Which I still love rereading to this day. I especially love reading the Astrix's to get all the jokes many of which just went over my head when I was younger. I also have a good sized collection of The Phantom (Diamond Comics) which are colourised versions of the original weekly strips which are hard or impossible to find anymore. I still miss even the * For the Ghost who walks, which seemed to appear nearly every page. Also have over a thousand Archie's Single and Double Digest's which we used to (and still do sometimes, though a little guiltily) Buy and read by the dozen. Oh and my Richie Rich's (which were next to impossible to get in Africa or India)