I know this is logistically ridiculous, but one time I had a teacher that was retiring, and for his last quarter of algorithms class he hired someone to record all of the lectures.

BEST CLASS EVER. I went to almost all of the lectures, but when I got home the video was usually already online - so if I missed something during the lecture, no worries, I could go back and rewatch it. IT WAS AWESOME.

Slides are terrible though - the problem is that it takes forever to make really good slides. I've seen it done before, and when it's done right it's a real piece of art, but 99% of the time slides are copied/made in haste and then the teacher just reads them off in class too quickly.

The only plus side to slides is you don't have to read the teacher's awful writing that is usually too small on a board that's too small for the giant room.