Sending a PDF to iBooks (iPad) How can I send a PDF to my iBooks in iPad without having to connect the iPad to my laptop using a cable?

Is this possible at all? Or do I necessarily have to use iTunes and a cable?
You can use


Mail
Dropbox
Google Drive
And many more


Basically you just need to be able to watch the pdf on your iPad in order to save and open it with iBooks also, you can still sync with iTunes