Credo is an online full text database of over 900 reference sources. You can search them all together to bring up a variety of articles related to a topic.
There are a lot of different kind of reference books out there that can help you find different kinds of information. You can find a number of relevant sources in the E184-185s and the JV6400s of the reference section. Below are a few of the examples we discussed in class, some of which are electronic sources:
Electronic Reference Books