I grew San Marzano a few years ago. I'm thinking maybe it was a "paste" tomato which is a type that is good for making sauce or paste but not necessarily great for eating fresh. I've not tried the mini San Marzano that Lin mentions though.
Biggest thing for tasty tomatoes is the longest day of full sun you can give them, plus of course enough water to size them up nicely. Don't grow them in the ground anywhere near trees, either. The tree roots will invade your tomato bed and suck up all the nutrients and water.
A great organic soil amendment that tomatoes really go for is alfalfa pellets - horse food. It's available at feeds stores in 50lb. bags for about $18. Be sure you're getting straight alfalfa, though. Some pellets for rabbits and such have vitamins, oils or other additives that you don't need. I add a couple of cups to each planting hole and mix it up with the surrounding soil before placing the plant in there. It releases some nitrogen at first for great foliage growth, then gradually peters out and just adds good organic texture to the soil. You do need to also use some complete organic fertilizer once the plants start to bloom.
