Softimage Mod Tool

Program used to make models for HL2.

XSI Mod Tool(Based on SOFTIMAGE|XSI Foundation) is available for FREE.

Official Website

Tutorials

XSI Beginner Tutorial

XSI Texturing

XSI Animation

Creating a Custom Character for Half-Life 2 Using the SOFTIMAGE XSI Mod Tool

VTM

3D Buzz - "Introduction to XSI" 5 hour VTM series

3D-Palace

Samples

SourceSDK contains various character/weapon/vehicle sample scenes(.scn) for XSI. See "sourcesdk_content/(game name)/modelsrc/..."

Also there is Korin XSI Mod Tool Scene data released by nkinta.