There are free obfuscators, including Dotfuscator Community Edition that comes with Visual Studio, and open-source obfuscators. See: [
^].
For a broad discussion of obfuscators including commerical ones see: [
http://stackoverflow.com/q/2525/133321[
^].
Obfuscators on Visual Studio Gallery: [
^].
Of course, CodeProject has resources you should examine:[
^].
All obfuscators are vulnerable to the efforts of hackers with motivation, skills, and software tools; imho, the best you can hope with any of them is to deter casual dis-assembly.
Richard Grimes has a free "workshop" on general .NET software security on-line here: [
^].
I'm curious: are you signing your assemblies ?