What kind of flowers (annuals) will be blooming the last week of July?

I am planning a wedding shower for my brother and his fiancee. I want to do centerpieces using some annuals planted in these cute little tins and buckets. I want to know what kind of short-medium sized flowers will be the best blooming for the end of July that I can get at a nursery. Want to have flowers, but don't want the florist... The date of the event is the 30th.