You can double your Dropbox referral credit to 500MB if you have .edu (School) email address. Schools without .edu domains are also eligible.
Get 500 MB instead of 250MB per friend you invite to Dropbox. That goes for everyone you’ve already referred too.
Create a new Dropbox account using .edu email address
or
Verify .edu email address if you already have Dropbox account.
australia.edu, newzealand.edu and england.edu offer free .edu email addresses
You can also get 1Gb with dropboxquest https://www.dropbox.com/dropquest2011/
and 750Mb here http://www.dropbox.com/free
Here is my referral by the way :p
http://db.tt/u3x9IBZ
Always have your stuff when you need it with @Dropbox. 2GB account is free!