Determinate tomatoes do quite well in containers - great drainage, warm soil.

Cucumbers, zucchini and herbs also are happy in containers.

Peas and lettuce do not seem to like containers.

Do people mix veggies or just grow one type in a pot - I've seen things like "salsa gardens" in green houses but wonder how they would fare in the "real world" [tomato, parsley, basil]. I would like to put some violas or some sort of trailing flowering plant in with a tomato or peppers, also a couple of herb plants. Would I need huge containers to do that [my containers are either 18 inches across the top by 24 inches high or 24 inches across the top x about 30 inches high]

Fern

Fern, last year I made up some mixed herb pots and they did very well. In a 2 gallon nursery pot I planted Italian Parsley, Summer Savory, Basil and Oregano. If you continually prune the herbs they don't outgrow their boundaries, look nice together and smells incredible. In 1 gallon nursery pots I also grew individually cinnamon basil, basil, lavender, and chili peppers. I grew a tumbling tom tomato in a raised 5 gallon nursery pot.

I think growing a tomato with herbs may not work as the tomato would require more moisture than the herbs, which are best kept a bit on the drier side. If plants require the same conditions then mixing them together in a container isn't an issue. Herbs need as much sunshine and fresh air as you can give them - the tomato might begin to shade them if they were grown togther. The roots get really warm when grown in containers so (I think) it's ideal method for growing stuff that likes those conditions. Also the root structures of herbs aren't huge - at least not if they're grown just for that one season - so you don't need as big a pot as you think. Tomatoes, on the other hand, is a completely different story.