The R.NET project provides a mechanism for communicating with R from a .NET application. This appears to be a promising way to create simple interfaces to some of the functionality of R.
Modern Applied Statistics with S (Statistics and Computing) W.N. Venables, B.D. Ripley
Interactive and Dynamic Graphics for Data Analysis: With R and GGobi (Use R) Dianne Cook, Deborah F. Swayne
Mixed-Effects Models in S and S-PLUS (Statistics and Computing) José Pinheiro, Douglas Bates