If you are looking for .Net assembly obfuscators, you might want to check out this open source obfuscator first: babel obfuscator. 

From the project's site:

Babel is an obfuscator for .NET assembly. At the moment It is a console based application.

Babel is based on Microsoft Phoenix framework. Phoenix is a framework for building compilers and numerous tools for program analysis, optimization, and testing.

Babel Obfuscator Features:

• Support NET Framework 1.1, 2.0, 3.5
• Obfuscate Namespace, Type (aslo generic types), Method, Events, Properties and Field
• Unicode Normalization
• Support Generic Types and Virtual Function Obfuscation
• MSIL Control Flow Obfuscation
• String Encryption
• Selective Obfuscation with XML Rule Files
• PDB File Generation
• Strong Name Signature