Tomatoes are probably the easiest to regrow without much effort and produces the largest yields of any fruit. To regrow tomatoes you simply need a ripe tomato, and some potting soil.
Cherry Tomato : slice in half, and squeeze out the seeds from the tomato into the soil, cover and keep watered. In about a week the sprouting tomato plants will come up. After the tomato plants develop you will need to thin or separate the plants. One cherry tomato can yield 6 to 10 new plants.
Basic Tomato : slice the tomato into quarters and remove the seed membrane. Place the seeds into the soil, and allow to germinate. Each quarter of the plant can yield as many as 10 to 15 plants.