Ball Blue Book of Preserving

If you are going to make jam, you need to have this. I'm new at jam making. I have some other books with more elaborate recipes, but I keep going back to this for basic information, ratios, instructions, etc. It covers pretty much every item you might want to preserve, with nothing elaborate or fancy.
It's not expensive, it's thin so it won't take up too much space on the bookshelf, and it will get abused. It's an essential reference.

This is a very reliable and useful book for canners. I tend to use this as a guide for ratios of acid/fruit or vegetable. Often I'll take a recipe and tweak the spices or other flavors and they have always come out sealed and I've never lost a batch of canned goods when using these directions.