Here is a post which lists quite a few good prebiotics, to give you an idea of what is out there. There is useful info on this website though it is interspersed with a lot of opinion which should not necessarily be taken as fact.
I think her idea that we should aim for a mixture of different types is good. Diversity of intake is associated with a more diverse gut flora and unfortunately western diets tend to be very low in prebiotic fibre.
Smallish amounts of 6-10 prebiotics is better than a large dose of just one.
There is also a thread which discusses many prebiotic and gut flora-related issues
here, but be warned, it is very long!