Dropbox is easily the most used app I have. I access it from my office PC, my MacBook Pro, my iPad, and my iPhone (and even my Droid X when I am using it). I love the ability to set up folders that I can share with friends, and the public links I can create for a file I want to share with everyone.
If you do not have a Dropbox account click here and sign up. By clicking here Dropbox will reward me with 500MB of FREE bonus space and if you get others to sign up you will get 500MB of FREE bonus space per person. I have used several other “in the cloud” file storage sites (I am currently checking out Google Drive) but this has been the best by far, and it is a pyramide sceme worth investing in…since it TOTALLY FREE!