There are probably hundreds of them, but only a few dozen related to Christianity. "-logy" comes from a Greek suffix having to do with knowledge. Contrast "-graphy", which is other kinds of study, such as haigiography, the study of saints.
Luckily, there's little "subtitles" to guide those of us (myself included) who can never remember all the formal terms; if you click on the main "theology" link, it has a list of the fora, and the descriptions of each.