The way I do it for my web site is to talk about each project in detail, what the initial customer need was, how we went about solving that need using code, a few screen shots or pictures of anything that lends credence that we actually worked on that project. Basically, same thing a web designer should be doing as well with their portfolio.
It's rarely about pretty pictures, focus on the results the customer wanted and you delivered... even if it was a school project.
They want to know the tech details, talk about that in the interview. What was the most technically complicated part of the project? What did you have to learn to solve that part? Bring paper and draw rough diagrams of how you went about it. You really can demonstrate programming abilities without ever writing a line of code in the interview... and a good interviewer will basically draw out this kind of information and use that to judge your fitness for the job.