I will join the borg, too. Large undergraduate lecture classes make class discussions difficult. So my latest "trick" in those classes is to open a discussion board within our university's online system. Each week I will open a new forum that fits the topic of that week. The most important part of this trick is to make contributions part of the grade and to specify rules for contributions.
The students can respond in several ways. They can 1. post a substantial question relating to the text, 2. answer a question posed by another student, 3. make a substantiated criticism of an argument in the readings for that week, 4. elaborate on an argument in the readings for that week, or 5. comment substantially on each others' comments in a friendly way. This approach usually lead to quite substantial online discussion among the students. Once in a while I will join in, make contributions, correct misunderstandings or answer questions. Sometimes I will answer the questions posted early in the week during the next class. Because participation in the online forum is part of the students' grade, only few students fail to contribute or fail to follow the rules. Occasionally a student will make a nasty comment but then you can go in and delete it or ask the student to edit it.
Though I implemented the online approach as a way to facilitate better classroom discussion in large lecture classes, the approach also works in smaller classes and graduate seminars. In smaller classes and graduate seminars the online discussion should not replace classroom discussion but be a continuation of it. In upper-level classes and graduate seminars students often develop a topic and thesis for their term papers during the online discussion.
One of main virtues of an online discussion forum is that shy students who don't speak up in class sometimes come out of their shell. This makes it easier for me to grade their contribution. Before I started using the online format, I would still make participation count toward their grade. But with classroom discussion only, I had a hard time grading those students who wrote great term papers but who were silent during every class. With the online discussion format, shyness or fear of public speaking is less of an issue, though I suppose students could have fear of speaking up even in a forum.