There are 3 to consider. You can get more expensive mics that are better and have more pickup patterns, but for PC use you only really need cardioid pickup. Unless you have 2 people podcasting from each side of a table, or other situations you are good with cardioid.
#1 - Modmic. It's a clip on 3.5mm mic for $50. It works well, is on your headphones so it won't pick up background or keyboard noise, and it has noise cancellation that works well. The sound quality isn't as good as better USB mics but it's pretty darn good for PC chatting.
#2 - Blue Snowball. $50 and good quality USB mic. Being USB it has no hiss unlike 3.5mm versions. To eliminate desk thumps and keyboard noise get the $25 chockmount for it, and a $25 deskmount or wall mount arm/boom. That'll turn it into a broadcast station type setup and get the mic off the desk and forward of the keyboard towards your mouth to eliminate backgorund noise.
#3 - Samson C01U. Similar to the blue snowball only it uses hypercardioid pickup. This eliminates keyboard noise a bit better. It's probably the better of the 3.
The most popular mic is the modmic, but that is only because people don't use shockmounts or arms with their mics. So they falsly believe the modmic is better. For the extra $50 or so for a shockmount and arm the Samson is the better choice, with the Blue Snowball also being good. Position the mic 6" form your mouth, and adjust the mic sensitivity to not pick up keyboard noise. People don't do this and just leave the standard mic on the desk and think it's garbage. Why do you think radio stations have the mics on an arm in a shockmount? It's not for looks.
You must buy the matching shockmount from either Samson or Blue. The microphone arm is pretty standard and the $25 ones are deskmount. You can get a bracket for $20 that screws to the wall and the deskmount arm will slip into that to make it more solid. Wall mount is more solid than a cheap desk clamp.
For ease of installation the modmic is king. Personally i use my headphones for music, movies, etc... so I don't want a mic attached to them. I prefer a desk mic on an arm I can swing out of the way when I don't want the mic. I don't want a mic and extra cable attached to my headphones all the time. For headphones that are strictly for gaming then the modmic is a good choice and the sound quality is pretty identical to the USB versions. Very high quality.