Adding attributes to vertices, and export

Hello experts,

I need to be able to define (either programmatically, or using the UI), add properties associated with each vertex in an object. This needs to be exported as a per-vertex attribute (for ex, like a normal or UV coord), for consumption by a GL engine.

What is the best way to add per-vertex attribute within Blender ? Please advise.

PS: this is my first post in the forums.