Here is a list of the most commonly used prom corsage flowers and their short descriptions and meaning:

Alstroemerias - Long, cylinder-like gray/green leaves with small star-shaped flowers in loose bunches.
The alstroemeria is a symbol of devotion and friendship.

Carnations/Mini Carnations - Hundreds of ruffled petals per flower head with a long, alternating leafed stem. Comes in a wide variety of colors.
Carnations represent fascination and distinction, and is a symbol for a woman.

Freesias - Little to no foliage, and 5-10 trumpet-shaped flowers with sword-shaped leaves. Comes in white, yellow, orange, red, pink, mauve, lavender, purple, and some bi-colors.
Freesias are a symbol of innocence and trust.

Dendrobium Orchid - Several sprays of dainty flowers on a slender stem (resemble daffodil in shape). Comes in white, magenta, purple, pink, green, red, and some striped variations.
The dendrobium orchid stands for love, nobility, and beauty.

Roses/Mini Roses/Sweetheart Roses - Long, alternating leaves and thorned stems. Most roses have 5 petals with 2 lobes per petal. 5 sepals grow below the petals. Large variety of colors and types available.
The rose represents love, passion, and perfection.

These flowers are the most used in making prom corsages, though there are many other smaller sized flowers that would be equally as beautiful in a corsage design.