Do I need more than 1 form of identification to get on an airplane? (within the US)

No - one government-issued ID is sufficient. Just make sure that your name as shown on the ID is identical to your name as shown on your boarding pass. Most people use either a passport or driver's license - here's a complete list of what's acceptable:

TSA: ID Requirements for Airport Checkpoints (http://www.tsa.gov/travelers/airtravel/acceptable_documents.shtm)

One is fine as long as they are government issued.