Tagging plugin ?

which recent plugin could be the best to handle a simple marketing
campaign ads app based on user profile tags ?
don't need sophisticated things :
- user profile -> tags created
-marketing campaign -> targets -> tag selection (from tags list)

thanks for your update

(Rails 2.3.5 / Ruby 1.8.7 moving asap to Rails 3 / Ruby 1.9 ..... so
the plugin must be ready for that.. )