I am looking for an implementation of the linear ballistic accumulator model or Ratcliff's diffusion model (e.g. in R, MATLAB, or Python).
Here are a few options. I have not tried them yet personally.
Scott Brown has a copy of Donkin et al (2009) on his web page with some code in R, Excel, and WinBUGS for fitting the LBA model:
The Diffussion model is available as a matlab toolbox called (DMAT).
For the diffusion model, there is also Eric-Jan Wagenmakers' "EZ-diffusion model", which you can find here.
This paper compares three different pieces of software for estimation of diffusion model parameters: