As mentioned the Google calendar is a great option, and depending on how good you are at code work its easy to create an I-Frame to make the calendar appear inside your website. If your really good with code then you can pass whats called an xml feed to your website that will allow you to customize the look and layout without frames. But if you just want a simple calendar code script check out this site. They have scripts, programs and much more in virtually any code base...most are open source and free as well.
Hot Scripts.