Depends on what you want to know. Unfortunately there are no detailed overview of the whole complex available in a single article or book. You will have to look up a lot of separate articles. Are you interested in any particular species or geographical areas? If you let me know I might be able to help you with a few references.

There are a book about the whole Trimeresurus-complex in the making (ie not only Trimeresurus but also related genera like Ermia, Ovophis, Protobothrops etc). It is being written by Gernot Vogel and Patrick David and as I understand it it will contain descriptions and extensive data on every species. Not sure exactly when it will be published though.

Here's a few of the more recent articles which deals with more than just a couple of the species. If you can get hold of them you'll find a lot of references in them which might be of further help to you.

A Phylogeny of the Trimeresurus Group of Pit Vipers: New Evidence from a Mitochondrial Gene Tree
Anita Malhotra & Roger S. Thorpe.
Molecular Phylogenetics and Evolution, 2000, 16(2)199–211.

Phylogeny, Taxonomy, and Biogeography of the Oriental Pitvipers of the Genus Trimeresurus (Reptilia: Viperidae: Crotalinae): A Molecular Perspective
Ming-Chung Tu et al.
Zoological Science, 2000, 17:1147-1157.

Nuclear and mtDNA Phylogenies of the Trimeresurus Complex: Implications for the Gene versus Species Tree Debate
Nicholas Giannasi, Anita Malhotra & Roger S. Thorpe.
Molecular Phylogenetics and Evolution, 2001, 19(1):57–66.

/Sundberg