Some of my favorite varieties below - Joy Bossi of "Joy in the Garden" recommended the white tomato, so I'm going to give it a "whirl" this summer!
1. Surround your plants with "Walls O Water." They can be purchased at most home or gardening centers. Before planting, walls should stand filled for at least 3 days to allow the water to heat up.
2. If you don't have time to wait for the Walls O Water to heat up, pour hot water into the soil area you will be planting your tomatoes.
3. Black plastic mulch is another way to warm up the ground. However, you'll still need to cover your plants at night if temperatures dip near freezing.