Math books are very cheap and very information dense. I'm going through Mendelson's "Introduction to Topology" right now. It's very good and cost only $10. Har

Math books are very cheap and very information dense. I'm going through Mendelson's "Introduction to Topology" right now. It's very good and cost only $10. Harmony by Walter Piston (and also "Twenty First Century Harmony," the book it inspired) is IMO one of the better books I've read on western music theory. I got my copy used for $20. SICP is nice to loan out (and also nice to read, it covers some pretty weird and advanced topics near the ends of the chapters), my girlfriend is going through my copy. ~$20. A couple Oreily books for whatever you're doing at work ~$120 (although double check, believe it or not there are a couple duds.) UML distilled by Martin Fowler is very good. ~$20? The art of electronics is a great book, I personally learned a lot from this kind of weird book titled "Basic Pulse Circuits" I found at a used book store for ~$10. Then leave the extra $100 for whatever interesting thing you find at good book stores (I've had the best luck in college towns in Appalachian Virginia.)