If you work with probability distributions a lot, you find there are multiple parameterizations (e.g., the two different forms of the exponential distribution), as well as interesting relationships (the geometric distribution is a discrete version of the exponential distribution). I have found Wikipedia to be a nice guide for some of this, but the coverage is uneven in quality. One of the Wikipedia links mentioned a new website, ProbOnto, that offers a systematic and standardized attempt to catalog every important probability distribution and the relationships among these distributions.
Maciej J Swat, Pierre Grenon, Sarala Wimalaratne. ProbOnto. Available in html format.