You can actually hook up several DS18B20's, which we have done...our Pi is monitoring indoor and outdoor temperature. Each sensor has an address, the Adafruit tutorial explains this pretty well.
Test out your webserver and modify your Python code to write the temperature to a file, say, temp.html every few minutes
Create an account on Trendy and point it at your Pi
This is easier than it sounds! To find numbers, Trendy just looks for whatever text you specify and the next number. So in our case, there was text in the HTML file saying "Shop temperature" and "Outdoor Temperature" and the following number was the number that Trendy tracks