Of all the methods devised to support tomato plants, nothing compares to homemade, solid, woven-wire towers.
Start with a roll of 4" x 4" or 6" x 6" woven wire fencing. Anything smaller than 4" x 4" makes it difficult to reach through the wires to harvest ripe fruit. Woven wire comes in widths ranging from 40" to 5' high: Get the widest you can find. Some garden centers sell fencing whose openings increase in size as they move upwards. That is, they start out with a row or two of openings measuring 2" x 4" then enlarge to 4" x 4" and eventually reaching as big as 6" x 8". Making towers with this size mesh is more time consuming, but it actually makes a more durable structure.
Cut a section 4' long with the end wires on one side sticking out without a vertical wire. Bend these wires into open hooks, about 1" long.
Roll the wire into a cylinder and use the hooks to grab the vertical wire on the far end. Then squeeze the hooks closed with pliers. That's all it takes.
To anchor the tower there are two options: You can cut the bottom horizontal wire off, which will provide the tower with 8 to 12 legs, 4" to 6" long. Merely push these into the ground and they will hold most plants with no danger of falling. If you use wire that increases in mesh size from bottom to top, this method will not work because the legs will be only 2" long - not enough to stabilize the tower.
Alternately, you can either stake or pin the tower in place. To pin it, bend heavy-duty wire, such as from a coat hanger, into a hairpin shape that's at least 6" long. Use three or four of these to anchor the tower in place.
For tomatoes, anchor the tower in place as soon as you transplant the seedlings. That way, none of the branches will grow too big before you get the support in place. Keep the seedling as centered as possible.
Tomato towers are useful for other plants as well. You can, for instance, plant a ring of pea seeds around an anchored tower, then train them to grow up the wire. This method works best with shorter-vined varieties. For longer vines, a trellis or A-frame support makes more sense.