Well, first of all, congrats on your pregnancy! I am so glad that you are going to keep your baby!

Sometimes writing a letter to your parents is a good idea because then they kind of have to 'hear you out'.
Another idea is to tell them while you are out at a restaurant for supper or something (hey, they can't exactly kill you in public, right?).
Other than that, you can just sit them down and tell them straight out.
If you go through the forums you will notice that there are a lot of posts about "Telling the parents" or "How to tell my parents", and if you look at those you can find a lot of advice.
Let us know how it works out, ok hun?