I need a Mic for making a Business Video

I'm going to be recording a business video for my work…
I have 2 DSLRs i'm going to be using for video (Canon Rebel T1i & Nikon D80)
I want good audio too though…
I've never used a mic before and I need a good one without breaking the bank.
What should I look for when buying a mic?
How will I know if its compatible to the cameras?
Please any info will help me.

I'm a graphic designer looking into my first video project.

You can look into some of these

Audio-Technica ATR-3350 Lavalier Omnidirectional Condenser Microphone

http://www.amazon.com/...B002HJ9PTO

Azden High-performance (SMX-10) Stereo Condenser Microphone

http://www.amazon.com/...B000GE403I

Azden WMS-PRO Wireless Microphone System

http://www.amazon.com/...B00006JPD8

Audio-Technica ATR-6550 Video Camera Condenser Shotgun Microphone

http://www.amazon.com/...B002GYPS3M

Rode VideoMic Directional Video Condenser Microphone w/Mount

http://www.amazon.com/...B0007U9SOC