I love the website Spaceflight Now. They provide detailed coverage on most rocket launches and have a nice worldwide rocket launch schedule. Unfortunately you have to look at it to not miss any launches. I would have loved to have the ability to import this schedule into my calendar, but searching the web did not find anything useful.
So I wrote my own parser for the Spaceflight Now launch schedule and provide it as a ics file.
If you want to keep getting updates just subscribe to the webcal.
In addition to providing a up to date launch schedule, this calendar also features recent launches.
Update: Due to recent changes, the current implementation does not work. In the meantime I recommend the webcal feed from Launch Library. Subscribe to it using this link.
As for the technical side of things: due to the way the Spaceflight Now website is coded and the not always consistent format of the launch events, some may be off either an hour or a whole day. So please be sure to check back on Spaceflight Now to have confirmation on the actual launch time.