With more than 5,000 R packages now available (from the CRAN and BioConductor repositories), for any statistical or data analysis procedure you can confidently say, "there's a package for that". To make it easier for SAS and SPSS users to find what they need in R, Bob Muenchen has updated his useful table of equivalent R packages for SAS and SPSS add-ons. For example, if you're doing conjoint analysis, the equivalent packages are:
Other categories of analysis include Operations Research, Power Analysis, Correspondence Analysis,& Structural Equation Modeling, Text Mining, Association Analysis , and many more. Note this only covers methods included in add-ons to SAS and SPSS, so some base-level functionality like survival analysis and mixed-effects modeling (also available for R), aren't listed here.
For the full list of R equivalents to SAS and SPSS add-ons, follow the link below.