Grow some Ailsa Craigs, because they're the best-tasting tomato there is. Moneyspinners grow lots, but you can buy them at the supermarket. You'll get a late crop if you plant from seed now, but I think it'd be worth it for a decent variety.
If you've got growbags, you probably don't need to start them in pots, but if you try any in open ground it's a very good idea. When they're up to your knees, Tomarite them frequently until the crop falls off.