brotherhood_of_LAN - 1:52 pm on Mar 6, 2013 (gmt 0)
I understand, and creating some site/service of your own and starting from scratch is a great position to be in.
The question is so open ended it is a bit hard for someone else to answer though. If you're going to create a new site and want to earn money through ads, try and find a niche with relatively less competition as some subject areas are very crowded with thousands of sites.
You could also try something a little more financially risky by purchasing an already existing website and develop it to its full potential.
If I personally were to think about building a 'service' a good place to start looking at is mobile services.