Borage, members of the onion family, basil, and asparagus are good companions

Here is a link that might be useful: Companion Plants

It's really not going to be as much space as you think once the plants fill in.

that being said, basil is supposedly a great companion plant for tomatoes, but honestly, I didn't see any tangible results from doing that, except that my basil didn't grow well. you may consider something that doesn't grow tall. Leaf lettuce, for instance, can benefit from the shade and won't compete for space.

Yeah, you're really not going to have much if any free space. Tomatoes will bush out pretty much as far as you will let them. Even properly caged you're looking at a plant thats probably going to hit a 3' diameter. If you plant at the very edges of your bed, you might be able to see where one plant ends and the other begins.

And they will completely shade the ground. I'll seconds the notion that by the time they're full size you won't have any room to spare.

Your plants are going to fill in, so never fear, you won't have a lot of wasted space. Best companions for tomatoes (to deter pests, improve tomato health, and enhance flavor) are basil, borage, chives, garlic, marigolds, nasturtium, mint and parsley. Use companions as frontage crops or "ground covers." Here's a list of best and worst companions for tomatoes.

Here is a link that might be useful: Best companion plants for tomatoes

I'll share a little more on my experience last year. I gave companion planting a run, and this is what I found:

I had no idea how huge my marigolds and nasturtiums were going to get in well tilled, fertilized soil. they were bush sized by the summer was over, and it made life difficult getting into my plants to harvest without serious pruning.

It certainly was colorful and pretty - however other than having more pollinators than i could shake a stick at, i didn't see any literal effects of the companion method.

pests were still there, disease still surfaced via bugs as well.

can herbs such as basil and others affect tomato and pepper flavor...the jury is still out on that. my palate may not be olympic caliber, but i certainly couldn't tell any difference among plants that had or did not have companion planting.

the best results i've heard have to do more with physicl benefits, such as lettuce growing early and getting some shade later on once the sun really heats up.

I have heard that it works to plant radishes with carrots... the radishes mature super fast and when you pull them it creates great space for the carrots to grow into as they mature later.

I understand that some people swear up and down by companion planting. i will likely always do it to some degree, but don't expect any miracles based solely on that.

if nothing else, it often brings variety and color to your garden, which is always a bonus in my book.

one last time: don't make the mistake of crowding, it's easy to do and a pain to deal with later on =)

-Rathos

IMO, 2 sq. ft. spacing is not enough. Minimum for my garden is 3 sq. ft. spacing, staggered. And quite frankly, I would not want my tomatoes to taste like mint, marigolds nor basil.

Thanks everyone. I'll probably try something small, herb like, on the peripheral.

I grow my tomatoes in 25 gallon pots that are 21 inches wide and 15 inches deep. Roots fill the container by the end of the season. I've grown marigolds, Basil, garlic, and nasturtiums as companions at one time or another. None of them did well. I don't know whether they kept pests away; I'm pretty sure they had no impact on flavor. I decided that tomatoes (and the companion plants) grow better if they don't have to compete for nutrients and light.

I resist planting marigolds for any reason because here they are a magnet for red spider.

Lemon basil thrives for me near my tomatoes, and I like to edge with nasturtiums. I don't get enormous nasturtiums there, but I have a raised bed and perhaps my soil is too rich. Marigolds get devoured by roly-polies so I have given up on them in the tomato bed. In the poor, dusty soil next to the garage is where I get monster nasturtium plants.