The best example would be Shu Qi turning down the role for Crouching Tiger, Hiden Dragon for some Pepsi commerical.
Others I can think of Ady An for taking all those second-leading role characters that are doing her no good ever since Dou Yu.
Ruby Lin for doing Qing Shen Shen Yu Meng Meng, even if it's "paying back a debt to Qiong Yao".
Vicki Zhao for the flag thing.
Any more? I'm sure there's lots lol.