you might want to take a look at the WIP headphonesµphones guide i started. its far from done but has some information regarding microphones you might want to read.
a cardioid microphone is directional so will help to block out the noise from your keyboard and mouse provided you do not have it next to them.
if you have the budget for it the at2020usb or at2020usb+ (+ version allows you to listen to your voice while you record, non + does not) are really great clear sounding mics.
the blue yeti is compareable but offers a few more options but is rather bulky in size and takes special mounts.
a monitor mount and pop filter are also suggested.
you may also want to read some of my other posts on the matter by googling (or using...