Freetag is an easy tagging and folksonomy-enabled plugin for use with MySQL-PHP applications. It allows you to create tags on existing database schemas, and access and manage your tags through a robust API.
Tag-normalization (lowercase, removal of non-alphanumeric chars) → searching for NY, ny and N.Y. will all find the same results
Raw-Format of tags is saved too
nice manual for how to implement Freetag into you own application on a database basis (needs unique db-identifiers as our project, release and file-ids could be)