I haven't gone through the website completely, but Jason Gorman appears to have some really good visual information on UML for .NET Developers.
UML tutorials aimed specifically at .NET developers, with code examples for most diagrams types:
- Class Diagrams
- Object & Sequence Diagrams
- Activity Diagrams
- Implementation Diagrams, Packages & Model Management
- Model Constraints & The Object Constraint Language (OCL)
Check out Jason's UML Diagrams here.