If you're interested in this kind of thing, Jon Bentley wrote a column called Programming Pearls which was later collected into books. One of the instalments was called Squeezing Space, and talked about stuff like this. He also discussed the trade-offs involved, as sometimes the code introduced to compress the data more than offsets the savings.
Even if most (if not all) problems in the book are something nobody cares about anymore in the industry, I still reccomend Programming Pearls to anyone writing code.
