Only two things that money can't buy
That's true love & homegrown tomatoes
~ "Homegrown Tomatoes," by Clark Guy
As far as it goes, Guy is right because by definition a homegrown tomato is a tomato you grow at home. I grew up on a farm and recall, as a kid, grabbing a salt shaker and heading down to the garden to pluck a perfectly ripe, sun-warmed tomato from the vine, and standing there sprinkling it with salt with the juices running down my chin. That's an experience you can't buy. I was fortunate enough to reprise this experience many years later when I was house-sitting for some friends with an extensive tomato plot and I again found myself standing in the garden gobbling down tomatoes.
I don't have a garden nor a place for even a pot - so no homegrown tomatoes for me. But fortunately you can buy the next best thing, someone else's tomatoes grown at their home.
I was interviewed once for a radio show in Chicago about Cooking for Two and the host and I got off on the subject of tomatoes. It's a subject so near and dear to my heart that a friend of mine refers to me as "Tomato Boy." Among other things, the interviewer asked me what "heirloom tomatoes" are.
What's an heirloom?
Strictly speaking an heirloom tomato is an old variety whose seeds have been preserved, over the years, as "heirlooms." Those seeds are preserved from years past primarily because the tomatoes taste good. Some are more acid than others, some sweeter, some have more pith and seeds, some less, some have a thin skin while others have a soft flesh. But ultimately it comes down to flavor.
The modern tomatoes sold fresh in supermarkets are not bred for flavor. They are bred to ripen all at once so they can be picked all at once. They are bred for uniform size so they're easy to pack. They're bred to be near perfect globes because we think that's an ideal tomato shape. They're bred to resist bruising (tough skin and tough flesh) so they can withstand shipping. They're bred to have a long shelf life. But they are not bred to taste good. And they don't.
Most heirloom tomatoes have at most one or two of the characteristics needed for a "good" commercial tomato. And most of them have great flavor. That's why the seeds have been saved. And very few genuine heirloom tomatoes can be found in a supermarket: you'll have to go to a farmers' market to buy them.
Some favorite heirlooms
Cherokee Purple: One of the world's ugliest tomatoes. It has dull purplish-red skin that looks like a horrible bruise. It also has lots of crevices in the surface. We're talking ugly here. But it has a delicate and very juicy flesh. I love it on a BLT because the juice soaks into the toast. A wonderful mess.
German Green: This tomato remains green when ripe (with perhaps a touch of red at the bottom) and has firm green flesh. The acid and sugar are perfectly balanced making it one of the best tomatoes for eating simply sliced with a bit of salt.
San Marzano: A famous Italian plum variety. It has a high flesh to pulp ratio and so is popular for canning - in fact you may be able to find cans of San Marzano at your supermarket - but I particularly like it for gazpacho.
Brandywine: This is an Amish breed dating back to around 1885. It's large beefy, well-balanced and good for almost anything. A real workhorse breed.
Caspian Pink: A pink-fleshed variety from Russia, it was "discovered by an employee of the Petoseed Company shortly after the cold war ended." It tends to the sweet side and is another great slicing tomato, but because of it's sweetness it handles a vinaigrette dressing well.
Tips
Never, never, never refrigerate a tomato. Some of the most complex and rich flavors deteriorate when a tomato is chilled and are not restored by warming. In addition, chilling makes the flesh mealy. I could explain the chemistry behind these changes - but won't. If tomatoes aren't quite ripe, setting them on a sunny window sill will speed and enhance ripening. If they're already ripe, store them out of the sun. Always store them stem-side down.
If you're lucky enough to have the space for a small garden, or even a suitably sunny porch for pots then you can produce your own homegrown, heirloom tomatoes. About.com's Guide to Organic Gardening has an image gallery of heirloom varieties with comments here. And it you find yourself wanting to peel a tomato you really should buy a serrated peeler.
When I die don't bury me
In a box in a cemetary
Out in the garden would be much better
I could be pushin' up homegrown tomatoes