Throughout my time on the net, making videos as well as writing, I have been into podcasting. Everyone knows that to be a good podcaster, you need a good microphone. Some of the microphones I have used vary from the traditional clip-on, desktop microphones, as well as condenser microphones.
If you are looking for optimal quality, and have a budget of up to $100, I would recommend the Samson C01U. It runs for about $80 and has amazing quality. You will want to buy the stand and the shockmount, which are about $40 total.
If you have a budget of about $30, I would recommend the Logitech USB desktop microphone which runs for only $20 on Amazon. It has good quality for a desktop microphone, but it doesn't sound like your voice, it sounds like someone talking, it is not recommended for podcasting.
Finally, if you just want a cheap microphone, I would recommend the Hands Free Clip on Mini Microphone which is only $5! They are cheap microphones, so be forewarned, you get what you pay for.
In general, when getting a microphone you pay for what you get.