From the Revolution Analystics blog at http://blog.revolutionanalytics.com/2010/08/distributions-in-r.html
One of the R language's most powerful features is its ability to deal with random distributions: not just generating random numbers from various distributions (based on a very powerful pseudo-random number generator), but also calculating densities, probabilities, and quintiles. John Cook provides a handy reference chart listing all of the distributions supported by standard R (reproduced below -- and there are many other distributions supported by contributed packages), and also explains the elegant naming scheme for the various functions.