You really have a wide range of choices. If you have the room, tools, and inclination, you can build a tomato "cage" that will accomodate virtually any size of indeterminate tomato. Or you can select determinate varieties that don't get over 3 or 4 ft tall. There are other threads here about "dwarf" varieties and the newer "ISI" (Indeterminate Short Internode) tomato types. But whatever you varieties you choose, the typical 3 ft. round ring is not a very good choice for anything but the smallest of plants.
I seen the Earthbox has a stake system you can buy seperately, but I bought Tomatoe Cages instead and was wondering if this was a good idea. Some of the plants are already almost to the top of the cages a little over 2 feet tall I'm guessing, but how tall do they usually get?