I love portulaca, otherwise known as moss rose. They come in full and colorful. Portulaca love the sun and seem to bloom all spring and summer long. Although the seeds are tiny and it may take a while to grow, it is worth the wait!
Although they are often regarded as common and old-fashioned, geraniums (pelagoniums) are one of the easiest to grow and most forgiving of poor conditions while producing loads of continuous colorful blooms. It's no wonder they are seen spilling from window boxes all over the world!