I use this to allow me to write on the screen. It's great for screencasting. I can circle important points or work problems in a very natural way. I bought mine on ebay for $35. If you're not interested in buying from ebay you can get a pretty good USB tablet from Amazon for around $60. Once you have your tablet you'll need to write on the screen:
Any video camera will have one built in. If you're recording using a cheap webcam then you may need a microphone to plug into your computer. Most laptops have a microphone built in already. You can get microphones for pretty cheap (under $10) if you're willing to buy from the internet. If you have a little extra I'd go for a USB microphone, they tend to have a better audio quality. This is not a necessity however, I went for a couple years with a $6 microphone.
While you don't need it, you might want to spend a litle on your microphone. I really like my USB Logitech headset. The audio quality is good and it's always the right distance from your mouth and I get virtually no pops. Lately I've been using my Guitar Hero microphone. It sounds good, but I have to be careful to avoid popping on my p's. This one was basically free. I just have to remember to hook it back up to the Wii before I try to play. You can get one for pretty cheap.
People often berate webcams as having too low of a resolution. To be fair they do. Most only have a resolution of 640x480 (about 1/3 of a megapixel). What people don't think about is that most free streaming hosting services on the net stream video out at 640x480 or lower. This means even cheap webcams are good enough. You should be able to get a webcam for under $30, assuming your laptop doesn't have one built in. Note: If you have a Mac, be very careful before buying a WebCam. Some older cameras that used to work with Macs will not work with OS 10.6. With Snow Leopard Apple removed support for webcams that require drivers to be installed.
These are digital camcorders that use tapes. They are definitely showing their age and are much less common then they were a few years ago. Next you need to see if you have an IEEE 1394 (Firewire) port. If both your computer and camera have this port you're set. I use my Mini-DV camera when I want to record directly into my computer. I also use it when I need to get a close up of something small (macro shot), particularly for electronics.
Most digital camers can take short videos. If the camera was bought in the last 5 years that video will probably be good enough. If it was bought within the last 3 years the video you can capture is undoubtedly good enough. The cool thing about these is that you can simply retireve the video in exactly the same way you get the pictures off. Simply upload the video to the net and you're done. For most people this is a "free" way to go as they already have a camera.
No matter what type of camera you go with you should invest in a cheap tripod (this will also help out your home videos). No one wants to watch the Blair Witch Project version of your lectures. If you don't have a tripod see if you can find some way to keep your camera from moving too much. This really is critical for smaller cameras like the Flip.