How to increase dropbox storage for free:
1) iOS / iPhoto Method:
|18GB free dropbox storage|
2) Referrals:Dropbox offers you 500 MB for each new referral you bring in (capped to 18GB). Invite your friends and signup via your referral and signup via your alternate email id's to expand your space. If you are lazy you can pay the guys at fiverr.com to expand your space to 18GB permanently for just $5. Consider this as it saves a lot of time. .edu referrals get double the bonus.
3) DropQuest Contest:Dropbox annualy hosts its dropquest contest where users have to solve puzzles to get free space. You get the space upgrade even if you are capped to 18GB. i.e. Even if you have 18GB you get + 1 GB (or more) added to your account for free permanently ! If you are lazy like me, just search for dropquest guides which help you finish the puzzles in record time sans the thinking. Check out the official dropbox blog for contest details.
If you know any other cool methods leave it in the comments below.