I really enjoyed CS186: Introduction to Databases, what classes should I take next if I want to continue in this field?
Try talking to your adviser.
CS 286B seems like the obvious one. If using the data in the databases to infer patterns and such is of interest to you, 188 and 189 may be relevant.
But it is a good idea to get a good background in the various areas of CS that will be important in industry or graduate school, such as 152, 161, 162, 168, 169, 170.