Aquamarine- Marina, Marine, or Aqua would all work to honor this gorgeous gemstone. Aquamarine symbolizes courage, so Brave would work as well.
Daffodil- Daffodil is an eccentric flower name, but don't let that stop you from using her.
Jonquil- However, Jonquil is the other name for Daffodils, and works nicely on a boy.
White- Some good white-inspired names are Snow, Ivory, and Lacy, though Snow seems a little out of place on a March baby.
Pisces- The Pisces symbol is a fish, so oceanic names like Pike, Roe, or Fisher would work nicely.
Aries- Aries itself works as a name, but if you want something a little more subtle, try Ariel or Ari.
Related to March:
Leo Names- March comes in like a lion, so why not use a Leo name? My favorites are Leo, Leopold, Leonie, and Leonardo.
March- March is a great month name, and one of the few that works better on boys.
Spring Names- March is the first month of Spring (hooray!), so any flower name would be perfect. Also consider Primavera, the Spanish word for Spring.
St. Patrick's Day- March 17th is St. Patrick's Day. Check out this list for ideas.