Hey guys, just wanted to let you know about this pretty nice website:
You can tell them the info from your last few periods, and they make a prediction for when your next one should be. It's pretty convenient, and the more dates you know the better they are able to predict; mine's been on the exact day they predicted the past two months. And, if you are working with Fertility Awareness, there's a setting for you to write in your body temperature. They also give you some stats about what phase of your cycle you are most likely in, and when you are most likely to ovulate - but don't necessarily believe these predictions, since every woman is different and they just give you the date when most women would ovulate.