This year I'm growing :

1) some unknown yellow tomato
2) purple prince
3) roma
4) bush beefstake
5) and one purple prince-yellow cross i created myself

I tried to cross the purple prince with the yellow last year and saved
the seeds. I'm growing them now though i'm not sure if the cross was
successful or it self-fertilized. I'll know soon enough when the
tomatoes on that plant get their color.

The year before that I crossed a beefstake variety of tomato with a
grape sized tomato and saved the seeds. I found out that you get a
ping-pong ball sized tomato from that! The gene/s for small sized
tomatoes appears to be dominant over large sized tomatoes.

I'm also doing another experiement this year. I saw this news clip on
grape wine yards in France. They mentioned that the grape growers
were very happy this summer. Aside from killing a whole bunch of
people, the hot, dry summer over there has helped produce a very good
crop of grapes. Because of the heat & dryness, the grapes have less
moisture in them and hence taste sweeter. Wines therefore will taste
better and be of higher quality (and command a higher price)

So i'm extending that same principle to tomatoes. I did not water the
tomato plants. I figure the fruits will also be less watery and more
full of flavor. Lets see if I'm right. So far the number of tomatoes
are down compared to last year but if they taste better, hell it will
be worth it.