Tomatoes and beans are good ones to save. They will occasionally cross, but not too often. And they are very worthwhile saving.

Jim

Potato-leaved tomatoes and currant tomatoes will cross easily, but regular leaved tomatoes won't very much, especially if you plant the different varieties across the garden from each other (and provided you don't live in an arid climate with nothing much else for the bees to forage). Bean crossing is a hot topic ~ some say they will, some say they won't. If you're not going to trade off the seed, I'd just plant those across the garden from each other also, and not plant ones with similar-colored seed very close at all since that'd make it harder to notice any accidental crossing over the years.

A good book on this subject is Seed to Seed by Suzanne Ashworth. It gives detailed info on what will cross with what and how to keep them from doing it. I just bought my third copy from Amazon for less than $17. (Let's see how long this one lasts before I find a fellow gardener I have to give it to. ;) )