Saving seeds from vegetables without expecting exact copies every time

I saved seeds from a particularly tasty tomato and planted a few out of curiosity. Then I remembered it might have been a hybrid, so the seedlings may not produce fruit identical to the parent. That's fine for an experiment; less fine if I'm counting on a reliable harvest. Which vegetables are easy for a casual gardener to save reasonably true-to-type seed from, and which need more attention to variety and cross-pollination?