Matlab provides a central tool for implementing complicated quantative financial models and is available to Caltech students for free through http://software.caltech.edu/. Here are some references on financial modeling with Matlab:
R is an open source scientific computing program with a broad and sophisticated user base. Here are some resources for getting started analyzing data with R.
Volatility Modeling and Risk Management
Asset Allocation and Portfolio Management
Derivatives and Financial Engineering
Financial News Resources
Macroeconomy and Finance
Quantitative Finance and Investing