U-drop crystal chandelier prisms are frequently found hanging from a chandelier's bobeche or top bowl. They refract light well and are inexpensive so they can be used when you need a lot of an item to fill out a chandelier. They are identified by the long narrow shape that looks like the tip of a narrow arrow. They do come in various sizes up to 6 inces or so and they come in a rainbow of colors.
ChandelierParts.com offers about 25 colors in many sizes. They are usually used with a top bead which might be the same color, different complimentary color or clear. They can also have a notch to add style and refract a bit more light.