Try to introduce some of the mainstream models....
For individual credit risk measurements:
-Probability of Default (PD) models: Moody's KMV RiskCalc Model (Logit/Probit) for private firms, Moody's KMV Expected Default Freqency(EDF) Model (structural Merton model) for public firms, S&P's Maximum Expected Utility (MEU) Model, Kamakura's Jarrow Model etc
- Loss Give Default (recovery) Model: Moody's KMV LossCalc
For portfolio model that produce the distribution of credit losses with expected and unexpected loss measures...
- Moody's KMV Portfolio Manager (Asset correlation)
-RiskMetrics' CreditMetrics (equity correlation and rating transition matrix)
-CSFB's CreditRisk+
-McKinsey's CreditPortfolioView