anyone want to explain what it is?! I want to get one maybe...

A teleconverter is a "lens" that you put between your camera body, and another lens. They have a glass element in them that magnifies the focal length of the lens you have it attached to. If you have a 2x teleconverter on a 100mm lens, your lens becomes a 200mm lens. If you have a 1.4x teleconverter on a 100mm lens, you lens becomes a 140mm lens.

You also loose some light when you add a teleconverter to your lens. You will loose 2 stops of light with a 2x TC, and 1 stop of light with a 1.4x TC. So if you have a 100mm f/2.8 lens and add a 2x TC to it, you now have a 200mm f/5.6 lens. A 1.4x TC on the same 100mm f/2.8 lens gives you a 140mm f/4 lens.

TC's are a great way to increase your focal length without spending a fortune and adding a ton of weight to your camera bag. They do have their drawbacks though. You loose light, and you will loose some image quality, espescially with a 2x TC. The image quality loss isn't as noticeable with a 1.4x TC from what I have read.

Another thing to keep in mind is that TC's work best with prime lenses. They will work with zooms, but you will get better results with a good prime lens. Also keep in mind that you get what you pay for. I have a cheap 2x TC that I rarely use because it degrades the image quality too much. Of course I'm using it on a consumer grade zoom lens...

I would recommend the Canon TC's but take a look at the specs on them. They are only designed to work with certain lenses.