These are delphiniums. One of my favorites! They come in shades of blue from a very pale sky blue all the way to a dark almost purple blue. They're great if you want to add height to centerpieces or other arrangements. Or you can take individual blossoms for bouts and corsages. I love the unique trumpet-shaped flowers - some say they look like dolphins (hence the name).
This corsage, also seen a few posts ago, combines some delphinium blossoms with bright blue cornflowers.
I absolutely love these little blossoms! Tweedia come in a fun shade of light blue, and while not really big enough to make an entire bouquet out of them, add some great color and texture.
Blue hydrangea - a classic. Great for centerpieces, or to fill out a bouquet.
Or if you're looking to make a brighter, bolder statement, consider some blue dendrobium orchids. But be aware that they don't grow this color - they take the purple and white dendros and dye them to make this bright shade, so you will probably end up with some purple in the petals (as you can see in this picture). Bu, they're still gorgeous!