Dropbox is fine, but you can run out of space. There is a free alternative which give you even bigger storage, copy.com!
You start with 15GB and for every user who creates an account via yours, you both get 5 GB storage extra, for free.
So, start creating an account with this link: https://copy.com?r=2ClF1N and get the default 15GB + 5 GB extra, because of using this link (and I get 5 GB free as well :) ).
Copy.com supports both Microsoft and Mac OS X environment!
Thanks and have a nice day!