Brad Garlinghouse, CEO
Capacity: 2 GB free; 5 GB for $9.99/month
What it's for: Sending files
Killer feature: Send massive files with return receipts and download tracking
Funding: $48.7 million
Number of users: 34 million
Fun fact: Used to produce Sesame Street
From new innovators to the old guard, these companies are experiencing phenomenal growth in the tech sector.