First, you will need a niconico account:
http://blog.kevinay.com/2008/07/how-to-make-a-nico-nico-douga-account/
Optional: Rikaichan is also useful since you can just highlight Japanese and it will show the meaning of the word in English. It's a firefox extension: http://www.polarcloud.com/rikaichan/
After you have a nico account, click one of the below links (or search for a vid yourself, you need to search for a game with a Japanese name though):
BlazBlu vids:
http://www.nicovideo.jp/search/%E3%83%96%E3%83%AC%E3%82%A4%E3%83%96%E3%83%AB%E3%83%BC
SF4:
http://www.nicovideo.jp/search/sf4
http://www.nicovideo.jp/search/%E3%82%B9%E3%83%88%E3%83%AA%E3%83%BC%E3%83%88%E3%83%95%E3%82%A1%E3%82%A4%E3%82%BF%E3%83%BC%E2%85%A3
http://www.nicovideo.jp/search/%E3%82%B9%E3%83%88%E3%83%AA%E3%83%BC%E3%83%88%E3%83%95%E3%82%A1%E3%82%A4%E3%82%BF%E3%83%BC4
Tatsunoko vs. Capcom:
http://www.nicovideo.jp/search/%E3%82%BF%E3%83%84%E3%82%AB%E3%83%97
http://www.nicovideo.jp/search/%E3%82%BF%E3%83%84%E3%83%8E%E3%82%B3+vs+capcom
http://www.nicovideo.jp/search/%E3%82%BF%E3%83%84%E3%83%8E%E3%82%B3vscapcom
Melty Blood:
http://www.nicovideo.jp/search/melty+blood
http://www.nicovideo.jp/search/%E3%83%A1%E3%83%AB%E3%83%86%E3%82%A3%E3%83%96%E3%83%A9%E3%83%83%E3%83%89
http://www.nicovideo.jp/search/mbaa
Mushihimesama Futari 1.5:
http://www.nicovideo.jp/search/%E8%99%AB%E5%A7%AB%E3%81%95%E3%81%BE%E3%81%B5%E3%81%9F%E3%82%8A
That's all I can think of right now. enjoy.
Not Nico but...
3rd Strike
http://youtube.com/theshend
http://youtube.com/gamersvision
http://youtube.com/truetech (find the "dat new hotness" playlist)
http://www.youtube.com/user/pruegel79 (just for the kuroda match videos)
http://www.youtube.com/user/AkumaKuroda (this years SBO finals/semis, more kuroda wank)
I can't find my way around nico sorry, but thought this was a good time/place to post these anyways :S