Rowntree, Derek. Teaching Through Self-Instruction: How to Develop Open Learning Materials (This is a very practical, easy to read book that explains a similar process to the one we use here for our print materials.)

Mager, Robert. Making Instruction Work. (This is sort of the opposite of the above, a more classic theoretical book that might not be what you want to read but that will give you a sense of what a behavioralist approach to instructional design is all about.)

Plus, the following is a really nice website, done by the Commonwealth of Learning, that also has some pointers to other references and resources.

http://www.col.org/Knowledge/ks_instrdesign.htm