I am often asked about courses after COS 109 -- courses that go deeper into CS or other aspects of computing, or other courses about technology and society. Here are some suggestions for Spring 2009. I don't have first-hand experience with most of these, but I know and can recommend the people teaching them. I'm happy to talk more about the courses, or help connect you with better sources of information than Course Offerings.
COS 116, The Computational Universe (ST). This course is not offered in Spring 2009 but would be worth looking at in a later year.
COS 126, General Computer Science (QR)
This is the basic intro course for CS majors, the certificate in applications of computing, the SEAS programming requirement, etc. If you liked the more technical end of 109 and found the programming more interesting than terrifying, 126 is a good bet; it's definitely the best way to take the next step if you think that CS or the certificate might be an option, or if you just want to try the next course.
FRS 120, Life on Mars -- Or Maybe Not (SA)
FRS 174 Fundamental Ideas of the Information Revolution: Insights into Technology, Language, and Biology (QR)
ELE 102, Hands-on Optical Engineering (ST)
ELE 391, The Wireless Revolution
ELE 491, High-Tech Entrepreneurship
MAT 199, Math Alive (QR)
PHY 115, Future Physics (QR or ST)
CEE 262, Structures and The Urban Environment (ST)