Until I finished my basement, my bookcase was made of concrete blocks and whith white laminated shelves that I bought at Home Depot. They were very strong and I would still have them if we did not have so many technical books in the attic. I just recommend placing them against a wall, to make sure nobody gets hurt. This concrete blocks have some openings that I use to place stuff, like CDs. The shelves will warp a little bit, but once in a while I would dust all the books and turn the shelves up side down. Even my sound system was placed there. They work really well.
Lucia