Three books on triggerplants have been written:
by Morren, early 19th century--only a few copies can be found in research libraries.
by Erickson, in the 1950's, reissued in the 1970's. Now out of print but often available from used book sellers. In the US, you can try Barnes and Noble.
by Darnowski, in 2002. You can buy a copy from him--just email for more information.
There is a rumor that Allen Lowrie is writing one as well, and if true, it should be as stunning as his books on the carnivorous plants of Western Australia.
For pictures of a wide range of species, please checkout FloraBase.
A very nice set of macro photographs from one of our French members.
There are many scientific papers on triggerplants, especially ones on the working of the trigger. There will be a bibliography here soon.