1885 illustration of a lentil plant, Wikipedia
Lentils and split peas aren't exactly beans, but they're often grouped with them, both in cookbooks and in the grocery store aisle. Cooking lentils and split peas is easy because they don't require soaking. As a bonus, many recipes calling for lentils and split peas, especially split peas, don't call for cooked peas, meaning you don't have to plan ahead as much.
Cooking lentils is easy! Pick them over and rinse as you would for dry beans. Toss into a pot of boiling water and simmer for 15-20 minutes, or until lentils are tender. Add your salt after cooking, or the lentils will take forever to soften. That's it; easy!
This is for the common brown lentil, the cheap kind that you usually find in the bean aisle. If you have another sort, cooking time will probably be different (and likely shorter). If you're using your lentils in a salad, you'll probably want a firmer texture; for soups, you might like them mushier.
One cup of dry lentils makes 2-3 cups cooked.
Cooking split peas
Cooking split peas is also easy, although it takes a bit longer. Again, pick them over and rinse well. Put in a pot of boiling water and simmer 45 minutes to 1 1/2 hours (according to this page). Some people advise soaking split peas, although it is not necessary; if you choose to soak, six hours will probably be sufficient (source).
Yellow split peas take longer to cook than green. Just like beans, cooking time can vary according to altitude, age of peas, water hardness, and soak time.