Another example of the wonders of the internet: the Metathesis website, whose centerpiece is the Metathesis Database.
What is metathesis? Metathesis is the phenomenon whereby two sounds that appear in a particular order in one form of a word occur in the reverse order in a related form of the word. [...] The goal of this research project is two-fold. The first is to provide a more solid empirical basis for the study of metathesis. To achieve this, we are developing a database of reported cases of metathesis. [...] (Note that not all reported cases of metathesis are actual cases of metathesis, as noted in some of the language listings.) The second aim of this project is to come to a clearer understanding of the nature of metathesis and, with this knowledge, develop a constrained and predictive theory of metathesis.
What a treasure for linguists! (Hat tip to Paul for the link.)