Not the first real mod I've started, but the first that I've finished.

New Third Person by Knowledge (Umpteen)

http://www.nexusmods.com/oblivion/mods/45754/

Requires OBSE, and CameraCommands.

This mod changes the behaviour of the camera. It adds a new third person mode with movement independent of the player, player movement relative to camera (inspired by third-person games like Dark Souls) and settings to tilt the camera to the left or the right of the player (over the shoulder camera). See the page on the Nexus for full readme.