I have done this with cheap camcorders and they work great! Currently, I use a Sony camcorder, and a Panasonic, and the only major difference is the brightness of the screen, which only bothers me outside in full sun. However, you are not going to be happy with footage of a presentation screen. There will be moire effects and other problems, and you are way better off getting a digital copy of the presentation PowerPoint or photos or whatever they are using, then editing those originals into your video.
In my experience doing this though, many speakers are incredibly boring to watch, and audio of what was said is way more important than video of the talking head. Your video cameras won't capture production-quality audio, but you can capture that separately by patching into the PA system. You'll obviously need to coordinate with the sound guy for that. They may be able to just give a recording, or you might need to bring your own equipment. ASK first, because some sound guys really don't like you messing with their equipment, and some are happy to hand you a patch cable.
Also, sounds like you're planning to do this for a conference? Many conferences already do very good quality recordings. Unless you're the guy doing that, you might ask about that - I prefer not to make videos when I can buy them :)
I am reluctant to suggest specific equipment because it will be out of date as soon as I submit my answer. I can confirm that many cheap camcorders do fine with business presentations, but I'm reluctant to suggest any specific models. Just look for the removable memory and batteries feature and get whatever seems like a good deal. Sony and Panasonic both have excellent imaging quality, but I prefer the Sony (it is one year newer which is probably the only difference).
Here's two pretty lousy examples:
- A presentation about 2.4GHz radio control systems.
- John Penny speaks about piloting the Rare Bear Reno Racer plane.
This is what you can acheive with cheap camcorders and no setup at all. If you have time to do setup, you could improve on this, but as you can see, video of the screen and the speaker aren't going to work together. I have also done video recording at a conference, but those are private. It came out better because I only recorded the speaker, and I had access to all the PowerPoint slides, which we edited into the video later at full quality. If you plan to do that, get a really smooth tripod and follow the speaker, or ask them to stay within your frame. Some speakers are really animated and they cover the entire front of the room walking around. That's going to be a problem for fixed shots. Tape on the ground can help the speakers stay in frame.