It's pretty easy to send just about anything to your Kindle, but if you're looking for an even more automated solution, Kindlebox does the job by linking a Dropbox folder to your Kindle and sending anything over automatically.
Once you authorise Kindlebox on both Dropbox and Amazon, you'll have a new folder in your Dropbox Apps folder. Put any PDF, MOBI, DOC or other type of Kindle-friendly file in there, and Kindlebox will send it over to your Kindle automatically. If you use both Dropbox and your Kindle a lot, this makes syncing the two up a lot easier. Unfortunately, you can't delete stuff directly from the Dropbox folder, but you can delete from your Kindle as normal.