Argyranthemum frutescens. Technically a tender perennial grown as an annual.
Pretty common in the plant trade, but frankly, not always the best plant for the East/Midwest, and definitely NOT good for the South during the heat of summer from what I've observed here in Michigan -- they do NOT like the heat. The warmer the summer the fewer the blooms. More of the kind of thing that would do well in very mild climates like S. California during the cool winter seasons.
Here's a link to the Proven Winners sight showing some of the different colors. Enter "Argyranthemum" into the search box to bring them up:
http://www.provenwinners.com/search/?cx=002434005836988681966:sl42cyduzso&cof=FORID:9&ie=UTF-8&q=ArgyranthemumUnfortunately, as I said, they are cool weather plants and do NOT bloom well during the summer. Daylength may be a factor as well. I've found they bloom in the spring, pretty much quit by mid-June with just a smattering of flowers, and then bloom again pretty well from Labor Day-ish until the frost takes them, which is usually late October here. They tolerate a pretty decent frost, but a hard freeze will usually do them in. I usually pick up just one or two for mixed containers every year because I'm a sucker for the colors, but I know they will spend most of the summer just as boring green bushes.
BTW, you CAN grow them indoors over the winter as a houseplant if you have very, very bright light and good ventilation to avoid mildew.