I just spent a couple minutes looking through one of the newer offerings from MIT's OpenCourseWare, and their Modal logic course looks quite good. They've got some neat exercises / problem sets (with solutions) and the lecture notes and handouts have a little more meat on them than the typical OCW module.
Click here to check it out.
Only problem is that one needs to purchase a textbook (or not, depending on how you feel about piracy) ...
Be sure to also check out OCW's Logic 1 and Logic 2 - both are really excellent resources and you can get away without any text book purchases because the lecture notes are the readings.
Now, go do some logic.