What small markets demand large databases?


I`m a skilled database developer and administrator looking to create a data driven online service.
I`m interested what could be the data intensive subject domains.
The idea is that the market should be small so that it is not interesting to big companies on the one hand and have high requirements to databases technical knowledge so that  average developers can`t enter it.
For example I built a phone directory in my country.
It contains rather big data set which makes it difficult to operate for average webmasters but I can do it easily and on another hand such niche is not interesting for big companies.

What small markets demand large databases?