wkhtmltopdf is what you need!
Basically, you need to call it from the command line, but you can easily integrate it to any web application using some server-side skills.
wkhtmltopdf.exe www.myhomepage.com myhomepage.pdf
The best thing is that you can also do that on session-dependent pages! The trick is that you have to capture your SessionID somehow and use it on the command line:
wkhtmltopdf.exe --cookie cookiename jahnvyp2yhcbi4sjxcrsnh3 "http://www.mywebpage.com/1234" mywebpage.pdf