Most people use Audacity for recording commentary then fraps for video recording.

Hardest thing to do is to sync the microphone to the video.

Another good alternative recorder is Bandicam. It's a great software and consumes less space on your hard drive.

I just use fraps to record both in game sounds and my voice, along with the video, that seems to work fine for me (It syncs automatically so you don't have to mess around with it) ... but I guess it's just whatever you like really but it does take up 4gb per 3 mins... so i think it's best to record on to a 1tb external hard drive dedicated to recording.

I usually record everything with XSplit.
Game, Game Audio, Vocal Audio, Webcam, ect.
You can also record your voice/game with Fraps.

FRAPS will work fine, if you can deal with the whole "it uses too much memory!" thing. (Other recorders (Ex. Screen Recorders) like, Camtasia Recorder and so will output some good quality as well.)
*REMEMBER* Better Quality -> More Memory.

As for the Audio, I'd recommend using Audacity. You will have to sync up the audio and video later on in the editing process. I don't understand why some people say it's difficult, its pretty easy if you know what you're doing. Once you record both your audio and video, and you're ready to start the introduction, do a little audio-sync test. For example, "Sync audio once you click the Options button in 3, 2, 1, click." Click the button (Option button in this case) at the same time you say click through your microphone. In the editing program, just move the audio until they sync pretty well. Doesn't matter if you're like, .25 of a second off, it'll still go well together. Once you've synced it up, cut out the Audio-sync part from the video, and start the video off with your introduction. (Ex. Hello everyone, and welcome to..)

I hope this helped you a bunch, I've been into recording/editing videos for about 3 years now, if you need some more help, don't fret to ask me on Youtube, or a personal message.