In addition to tomatoes, we've planted peppers, eggplant , cucumbers, zucchini, squash, snow peas, bush and pole beans and a few more herbs. That's a lot for our dinky little garden but everything is on "proper" spacing. That - according to Square Foot Gardening by Mel Bartholomew. This book has become our vegetable planting guide and we follow the spacing recommendations religiously. That being said - I don't really like this book. Mel seems... well let's just say he doesn't lack any self confidence. My general opinion on such matters is - people who think they know everything irritate the hell outta those of us that do!
Of course when we need a definitive answer to a vegetable gardening question there's still only one place to go. Sammy Don Cotner's Vegetable Book. Sam was a great guy and his book is a living legacy, proving he was and always will be a Texas Hort Hero.