The Judge Dee series by Robert van Gulik

Ok, you know these already, but they are marvellous! Set in ancient China, written in the fifties and sixties by eminent Sinologist who was also Dutch ambassador to the PRC.

The Firemaker by Peter May

Thriller set in modern Beijing. Plenty of detail -- the author has researched the Beijing police force in great degree -- and a true thriller plot: comparative innocents stumble across a terrible conspiracy that threatens to destroy both them and many others. 

Playing for Thrills by Wang Shuo

Off the wall crime novel by young enfant terrible of modern Chinese literature. If you liked the movie Beijing Bastards, you'll enjoy this. If you prefer Dame Agatha, probably best avoid.

The Flower Net by Lisa See

Another thriller set in Beijing. Author is American-born Chinese.

God's Chinese Son by Johnathan Spence

Excellent history of the rebellion.

The Devil Soldier by Caleb Carr

An American who joined up to fight against the Taipings.

Taiping Tianguo by Augustus F Lindley

Marvellous Victorian adventure yarn of angry young Brit who joined the Taipings.

There are lots!

China Wakes by Nicholas Kristof and Sheryl Wu Dunn is recommended.