Drew Houston, CEO
Capacity: 2 GB free; 100 GB for $10/month
What it's for: Backups
Killer feature: Syncs folders automatically on several devices
Funding: $257 million
Number of users: 50 million
Fun fact: will.i.am is a fan
NEXT: YouSendIt
From new innovators to the old guard, these companies are experiencing phenomenal growth in the tech sector.