Yes, tomato plants should be pruned for optimal fruiting. Unless they are "determinate" plants which grow to a certain length and then stop; in which case they don't need pruning.

My tomato plants are beef steak, and million bells, or thousand bells, or bejillion bells, whatever they're called =:)

As far as I know, these types aren't determinate, are they?

Probably Sweet Millions? Cherry type tomato? Those are completely indeterminate. Most if not all beefsteaks need pruning too.

Sweet millions cherry tomato is an indeterminate or vining tomato. Bush beef steak is a determinate or bush tomato.

Vining tomatoes will grow very tall. I think sweet million grows 10 feet. Vining tomatoes should have the suckers trimmed, but never trim suckers from bush tomatoes.

If you trim the tops of vining tomatoes they stop growing so you will only get the fruit that is on them now. I know gardeners who do this to ripen the fruit on the vine.

I never even thought of trimming bush tomatoes so I don't know what will happen but I imagine they would stop growing too.

Trimming won't hurt them, but if the part you are trimming off has blossoms or young fruit then be aware you may be giving up some fruit. Then again, at this stage in the season who knows how much more fruit will develop anyway and it sounds like your zucchini could use the light. Due to our cloudy, rainy and cool summer, I'm just leaving any wild growth on my tomatoes hoping for more fruit, though who knows if those blossoms will even mature into fruit in time for frosts. I did have 3 ripe tomatoes but now there's a big gap waiting for more fruit to develop.

Only do that to interdeterminates. Be sure to let a few suckers grow from the bottom. Support them if needed. The suckers will take over the role of producing flowers and fruit but whether they will do so before frost is another issue. What you can do, especially if you live in a city or sheltered area, is weather the first few frosts by covering them with frost cloth or floating row covers. This is easier if your plants are short and bushy. Take advantage of the warmth we sometimes get in late September.

I don't like pruning tomatoes, even indeterminates. It's good if you want to squeeze out efficient, early, maximum production per square foot but not if you just want healthy, productive plants that produce all season. This short, wet, crappy summer was ideal for pruning plants, but a long hot, dry summer (2006) would not be.