Minecraft Lets Plays are amazing, I can't think of any other game where it spawned such a large community. For people who want to watch a little bit more serious Lets Plays (not just targeted at toddlers) I recommend the MindCrack[0] server/network of Youtubers. In particular EthosLab[1]. There is also a large community around the ForgeCraft[2] server where most major mod creators play and test their mods. Direwolf20[3] in particular.

[0] http://www.guudelp.com/

[1] https://www.youtube.com/user/EthosLab

[2] http://www.reddit.com/r/forgecraft/

[3] https://www.youtube.com/user/direwolf20