Portulaca?

I think you might be looking in the wrong place...think perennial, not annual plants. That is where you will find the most drought-tolerant. I would suggest Centaurea (Bachelor's Buttons). They adapt well to pots, are available in a variety of colors and, in my opinion, are simply very pretty. They will also tolerate full sun to partial shade and are a perennial down to zone 3. You may even be able to overwinter your potted plants with a little bit of protection. Hope this helps. :)

Here is a link that might be useful: Bachelor's Buttons

Thanks for the advice. I've never had moss roses but maybe that would be worth a try. I've never planted perennials in a pot, only in the ground so I guess that's worth a try to if I can find something that blooms all summer. I have a nice book on Minnesota perennials so I'll take a closer look at that with pots in mind. I remember my mom having bachelor buttons in her garden when I was a kid and I liked them. I don't think I've seen them around since but I'm not around a lot of gardens.

Angelonia! It's a tender perennial grown as an annual in all but the warmest locations. This sun loving perennial blooms non-stop until frost, needs no deadheading, loves the heat. The size is more than 24x24 fully grown....which it achieves pretty quickly.

I second both portulaca and Angelonia. You might want to check into echinacea. The new Cheyenne Spirit is supposed to repeat bloom all season without deadheading. I am growing it for the first time this year. Salvias are an all summer bloomer that don't mind heat or some drought. It would be hard to beat Victoria or Mystic Spires. You could also try Vinca. They are tough too. Of all these on the list, portulaca is the most drought tolerant of all in my experience.

Hope it does!

Hope it works for you. I like the portulaca because of its flowers (as you said, I also agree that it looks quite pretty), as well as the fact that it makes long trailing stems that are just perfect for trimming and sticking it in the ground or another pot somewhere to make more portulaca plants.