Here are some tools to help implementing BDD:
BOO - Specter: A tool written for the Boo language, a .Net and Mono programming language.
C - CSpec
C# .Net - NSpec
.Net - NBehave
.Net - NSpecify (incomplete site)
Delphi - dSpec
Groovy - GSpec, http://easyb.org easyb, tspec a non-English BDD framework with Thai syntax.
Java - JBehave, JDave, beanSpec, Instinct, GivWenZen (Java and FitNesse)
PHP - PHPSpec
Python - Specipy, spec plugin for nose
Ruby - RSpec, Shoulda, test-spec & bacon, Cucumber
Scala - Specs
Smalltalk - SSpec