If students will be using it I'd avoid anything with a touchscreen or hard drive. DVD cameras are a general pain and I wouldn't recommend them in any situation.The students in our Video class use the Panasonic GS## (we update regularly) and they have worked out quite well for us.
Depending on your intended use you might find the rapidly improving solid-state memory cameras (Flip seems to be the most popular brand right now) a good fit for the classroom. You wouldn't be making DVD quality vids but they'd be good enough for web posting, easily. They are about half the price of even the lowest end DV-Cameras and far more sturdy.
Unless you need DVD quality movies, I would avoid ones that use tape. Taking a five minute movie off of a tape and making it into a Quicktime Movie, can take almost 2 hours (using IMovie). Using one of the memory card video cameras (or Flip and others like it), produce movies that are already in a viewable format (like AVI, QT or MOV, depending on camera). The videos can then be put into Movie Maker or IMovie and be edited. And for the price, you could probably get two or three cameras for your classroom, instead of one. You will spend more time making movies, producing content and less time waiting for the rendering to take place. You will also be able to shoot a video and post it to a web server in one class period (actually a five minute video can be posted in less that one minute, so you could shoot and post in a total combined time of six minutes or so!). But if you need the quality for some reason, then the tape ones, with the memory stick (make sure you can record video to memory stick, and not just pictures) would probably be the way to go.