I'm looking for a desktop microphone to pair with a Superlux HD668B. Preferable $20 or under but I want to make sure I don't buy a piece of crap. We all know there's tons of them out there.
Any mic at $20 is probably going to sound pretty bad. If you have a decent android phone you can use its mic through an app. Pretty sure its called WO Mic.
I'm not sure any desktop mic is worth buying that's in that price range.
Maybe just pick up the zalman clip-on and call it a day? I've heard a streamer use it and it sounded quite good.
I was just looking at that one. It might be ok for the time being
I only ever buy cheap mics that have the windsock on them.. the little foam thing, I think it makes a pretty big difference as far as filtering out background noise and such. People on discord/TS say they sound good so thats good enough for me.
Do you have a link for them?
I can find, but they are actually headsets.
As Logan stated long long time ago in his gaming headstuff under 50$, Zalman zm-mic1 for 7-8$... Sounds OK for 7-8$ and even If you pay 20-25 you will get the same quality... 
I guess this is the Zalman clip on mic you guys mentioned...
I have the Zalman mic. It picks up everything around the mic but other than that people can hear you well enough although you sound a bit distant but that's due to the location that its being attach to your headphone cable and not close to your mouth.
You can use the zalman clip on like suggested i have one but im very annoyed by it you could get a Takstar pcm 1200 a desktop mic that's cheap like $20 but not usb if you want something desktop save up to $50 and get like a blue snowball or a CAD GXL 2400
Takstar http://www.amazon.com/PCM-1200-Professional-Microphones-Internet-Mic-Black/dp/B00K7C9EJY