The list I have is fairly close to sniles' but it's not just about GDP:

Tier 1
Beijing, Shanghai, Guangzhou, Shenzhen

Tier 2 (Upper)
Tianjin, Chengdu, Chongqing, Wuhan, Hangzhou, Suzhou, Nanjing, Dalian, Shenyang

Tier 2 (Lower)
Xi'an, Qingdao, Ningbo, Xiamen

Tier 3 (Upper)
Jinan, Zhengzhou, Hefei, Wuxi, Changsha, Dongguan

Tier 3 (Lower)
Harbin, Changchun, Changzhou, Nantong, Fuzhou, Kunming, Nanning

Tier 4--a real mixed bag
Urumqi, Xining, Lanzhou, Yinchuan, Hohhot, Taiyuan, Shijiazhuang, Luoyang, Nanchang, Guiyang, Haikou

Takeaway: there is a lot of potential (= opportunity) for those willing to live/work/invest in the Tier 3 and 4 cities.