Hi Travis,
There's quite a few threads about it, but they can be fiddly to find.
squash and
peppers
These two families are
almost guaranteed to cross, and I'd be looking at avoiding cross-pollination through things like barriers or species selection rather than distance.
I'd suggest sticking to one variety of corn unless you have a huge amount of room. It's wind-pollinated and pollen can go for miles.
Corn has
another issue to keep in mind.
Many brassica (cabbage family) cross madly; the easiest way I've found with them is to try and stagger flowering.
Beets and chard cross easily and you end up with nothing in particular
Major things I don't worry about: lettuces, tomatoes, beans, herbs.
There's plenty more.
I recommend Suzanne Ashworth's 'Seed to Seed'. It's quite technical and very thorough.