How about a series of speed tests to assess data access.
Relational databases; SQL Server, MS Access, MYSql.
Text based; XML, CSV, JSon.
Google's Big Table, Amazon SimpleDB.
There are cloud database solutions.
You could choose as many as you wanted and felt comfortable with.
Work out the tests - perhaps a series of simple string searches, a series of relationally bases queries, again, as many as you have time for. Speed of insertions, retrievals, changes and deletions. Managing images... There are lots of options.
A key benefit is familiarisation with several databases - perhaps one that a potential employer may use.