Better Homes and Gardens maintains a directory of common garden flowers on its website. For names of wildflowers, it is best to consult sources that are tailored to a specific region.
The Better Homes and Gardens website, BHG.com, is an excellent source for names, pictures and growing information on an assortment of garden flowers. The information is searchable by plant type, growth characteristics and special features of the plant.
For information on wildflowers, it is best to identify a particular region of interest due to the vast number plant species. For example, GoBotany offers a simple key for identifying wildflowers specific to New England. IllinoisWildflower.info has information on flowers native to Illinois and the Midwest, organized by habitat type and growth characteristics.