For rapper/R & B, check out Pan Wei Bo(Wilber Pan) because he's called "the new prince of Chinese rap/r & b" or something like that. Try his song Bu De Bu Ai.
You should also try Wang Lee Hom and Jay Chou.

nan quan ma ma, jay chou, relax one, alicia chen, cyndi wang, jolin tsai, f.i.r., elva hsiao, landy, michelle & vickie,

mainland china music is not bad..

i recommend Na Ying.. her voice just blew me away!

other mainland artists that are quite popular in China are Han Hong, Sun Nan, Liang Liang, Dao Lang...

the only group i know is Mr. Flower (Hua Er Yue Due) .. not sure if they are from mainland tho..but their song 嘻唰唰 (Xi Shuai Shuai :S hope i got the pinyin right there) is quite catchy :)

What about Sammi?

:roflmao