To learn English, you can check out these 10 YouTube channels, to learn Chinese, you can check out these 10 YouTube channels, and to learn Japanese, you can check out below 10 YouTube channels, which have many subscribers and offer some interesting Japanese lessons.
1. Japanesepod101
Channel Views: 133,526
Joined: August 06, 2006
Subscribers: 19,248
Videos: 165
Produced by JapanesePod101.com, this YouTube channel will show you how to speak, read, write and hear Japanese.
2. Thatjapanesegirl
Channel Views: 130,873
Joined: January 29, 2009
Subscribers: 19,408
Videos: 72
That Japanese girl will show you some interesting Japanese video lessons.
3. Gimmeaflakeman
Channel Views: 243,420
Joined: March 03, 2007
Subscribers: 10,586
Videos: 420
This is a gathering place for YouTube Japanese vloggers, so you can watch different styles of Japanese video lessons.
4. Hikosaemon
Channel Views: 177,934
Joined: February 28, 2008
Subscribers: 16,287
Videos: 113
With this YouTube channel, you can learn both Japanese and English, since there are both Japanese and English subtitles for every video, whether it is spoken in Japanese or English.
5. GenkiJapanNet
Channel Views: 259,417
Joined: March 04, 2007
Subscribers: 16,614
Videos: 138
Most of the videos in this Youtube channel are songs or games.
6. Thejapanshop
Channel Views: 78,099
Joined: December 07, 2006
Subscribers: 7,467
Videos: 73
There are tens of video lessons with different teaching methods in the thejapanshop’s channel.
7. Aploosh
Channel Views: 67,317
Joined: January 13, 2007
Subscribers: 2,526
Videos: 138
You can watch the situational dialogues and learn phrases, sentences, grammars and some other Japanese knowledge or skills.
8. Sodapencil
Channel Views: 38,747
Joined: March 27, 2006
Subscribers: 2,500
Videos: 119
This YouTube channel is launched by Kaoru, who is a 38 years old Japanese teacher in Melbourne, Australia.
9. Yesjapan
Channel Views: 51,977
Joined: February 12, 2006
Subscribers: 3,584
Videos: 25
The teacher George Trombley and his Japanese co-hosts bring their irreverence and high-energy approach to the real and present-day Japanese.
10. LetsLearnJapanese
Channel Views: 15,943
Joined: December 06, 2007
Subscribers: 1,149
Videos: 10
There are only 10 videos, but you can watch them and learn Japanese by singing songs.
The above 10 YouTube channels are free for you to learn Japanese language, you can check them out and see if some of them are useful for you.
By the way, the numbers of channel views, subscribers and videos are based upon May 7, 2010 and they may be increased now. 
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One Comment
All these sites listed are great but I want to add one more teacher to the list! This youtube teacher has some excellent video lessons! She is easy to understand and provides detailed but easy to follow lessons. I have learned more from her in two months than I did taking a Japanese class (which cost me 500 bucks! grr)..anyways I recommend her to anyone looking to learn some Japanese.
http://www.youtube.com/user/CatwomanJolie