Which schools are known for graduation level database research?
MIT is the home of Michael Stonebraker, probably the leading RDBMS researcher working in academia today. A lot of the research is done in private labs tho', e.g. CJ Date and Ted Codd did much of their early work at IBM.

I am missing a huge amount here as I am only really interested in RDBMS research; there's probably a lot more going on in OODBMS research.