From Valve Developer Community
$ssbump(New with Half-Life 2: Episode Two / Source 2007)
- Self-shadowing bumpmapping.
- Color tinting.
- Use this material as a decal.
- Detail texturing.
$distancealpha(New with Half-Life 2: Episode Two / Source 2007)
- Vector-like edge filtering.
- Specular reflections.
$lightwarptexture(New with Half-Life 2: Episode One / Source 2006)
- Per-texel color modification via a warp texture.
$seamless_scale(New with Half-Life 2: Episode Two / Source 2007)
- Mitigation for displacement texture stretching.
- Expensive and cheap transparency.
$phong(New with Counter-Strike: Global Offensive)
- Diffuse reflections. only.