Amazon provides an app Send To Kindle in both PC and Mac versions and also provides browser extensions as well.
This is pretty cool app that allows you to send a PDF file directly to you kindle device or even to your kindle app on iPad. It especially saves a lot of trouble if you are using iPad kindle like me.
The desktop application is available for both PC and Mac at the link www.amazon.com/sendtokindle.
SendToKindle from Explorer
The browser extension allows you to directly send a web article to your kindle device or kindle on iPad. This is very much similar to what you can achieve using instapaper, but for free 🙂
I wish there is a similar technique to send a epub file directly to iBooks instead of going thru Dropbox/sugarsync or iTunes sync.