I just purchased a hanging basket of Supertunias because it says no deadheading.

I did Million Belles last year not very heat tolerant and I am only in RI and still durning the summer it wilted so maybe the Supertunias will do better

I've never thought of Petunias as heat tolerant....at all. But I have read that some of the newer hybrids are better, such as the Tidal Waves™.

I should have added my suggestions for your hanging baskets. See if you can find Scaevola, called "fan flower". Its adorable blue flowers continue on in the heat of summer, all summer as long as they grow in full (or mostly full) sun.

Another favorite of mine is the Portulaca oleraca hybrids. Wow!

For cascading petunias, a popular choice is 'Pink Bubble Gum'. This variety is commonly used in municipal and commercial plantings -- they are little growing machines! You may even have to prune them back more than once.

Along with the petunias, you (or others) may want to look into various water retaining devices to help keep your baskets hydrated. If they dry out for any reason, be sure you have rewetted the soil completely or the water will run through and seem watered, but in fact may still be dry. I use food grade yucca extract in barely lukewarm water to rehydrate the dried out potting soil -- it has to be added at the END of filling the watering can, or it creates billowing suds.

For me, petunias are quite heat tolerant though require quite a bit of water. Do keep in mine, though, that I'm in zone 6 which may make a difference.

@Saturn333, you did say heat tolerant, but did you mean something that will require less watering? If that's the case, the suggested Portulaca will go longer without water. The flowers do close at night at least on some varieties. Million Bells will take both cooler weather and hot weather, but yes, they do require probably daily watering as Paul MI mentions. They won't cascade as far as the petunia I mentioned (nor will Portulaca).

Scaevola now comes in a variety of colors -- I just bought some bright pink

http://suntoryflowers.com/variety/surdiva-classic-pink/, but it also comes in white, several versions in blue, and even pale yellow.

http://c0380802.cdn2.cloudfiles.rackspacecloud.com/6797-Suntastic-Yellow-Scaevola.jpg

This plant can be used in full or part sun.