Widgets
One can consider developing widgets for blogs/social networks for monetizing.
Widgets or gadgets are plugins to blog/social networks, which bring in information from external network and display inside the internal network.
Widgets can be considered to fall in following categories:
– Informational: RSS readers, clocks, countdowns, stock ticker, etc.
– Games: classic arcade, simplistic sports, arade bowling, etc.
– Utility: geolocation, visitor statistics, etc
– Silly: Penut Butter Jelly Time
– Interactive: chat based, message ability, user content, sliders, etc.
Think of idea which will set you apart in one of above categories.