Mandopop: Pang Mailang (龐麥郎)

From the start, it should be obvious to even non-mandarin speakers that Pang can't sing. He also sings with a strong southern dialect, and off-beat... And the song is about a pair of skateboard shoes he desperately longs for... This is a really big viral hit in China, and has given new defintion to the term "diaosi" (屌丝), in a very modern and ironic way, with people loving to do various interpretations of it in a somehow loving way when something that everyone can relate to is described in such a humiliating way. Combine this with a media campaign where his age and background is fabricated in an obvious way to invite specualtion (also, observe the video - it's obviously much more calculated than one would think at first) and you have here a kind of phenomena that is another sign of China being very much a modern place (yees, it's not just positive, I know... ;-P)

• Pang Mailang - My Skateboard Shoes (我的滑板鞋)

Mandopop: Chopstick Brothers (筷子兄弟) - Little Apple (Xiao Pingo/小蘋果)

"Little Apple" will probably be one of the biggest chinese-sung viral hits of 2014, from the comedy duo Chopstick Brothers. The refrain is about loving his little apple (which has language connotations to do with the forbidden fruit theme in the video). For some other example of their production, see their (english subbed) Old Boys or the more serious "Father".
update: yes, they was indeed the no 1 hit in China 2014. In July 2015 they released the follow up, Little Fruit. I actually think this will be quite successful too.

• Chopstick Brothers - Little Apple (小蘋果)
• Chopstick Brothers - Little Fruit
• T-ara with Chopstick Borthers - Little Apple
• AK人聲 - Little Apple (cover)
• Nurses do Little Apple
• Flash mob in Beijing - Little Apple
• Meng sisters edition of Little Apple (wait for special version at 2:10…)
• Chopstick Brothers - Old Boys
• Chopstick Brothers - Father (父親)