Senate_analyses is a project mainly written in R and RUBY, it's free.
Statistical Analyses of the U.S. Senate
Source code for my analyses of Senate roll calls. Currently, only the most basic ideal point analyses are implemented.
To resolve the inherent indeterminacy between assigning Republicans positive numbers and Democrats positive numbers, Senator Coburn (R OK) has been assigned a hardcoded ideal point of 2. While I consider a better solution, I am holding off estimating ideal points for earlier congresses.
All of the roll call data comes from VoteView. If you use their data, please cite them, because their remarkable efforts are what makes it possible to analyze roll call records so easily.
If you'd like to start using this code as a basis for your own work, you'll need to have R installed along with the ProjectTemplate, pscl, ggplot2 and rjags packages available on CRAN. In addition, you will need to have JAGS installed, as the ideal point model itself is currently implemented as a JAGS model.
For details on the underlying mathematics, both Simon Jackman and Andrew Gelman have written books that contain very clear descriptions of ideal point models.