One fanfiction that comes to mind is http://www.fanfiction.net/s/3645494/1/Twist_of_Fate, a massive, novel-length,
completed fanfiction over at fanfic.net.
That said, there are a lot of decent fanfictions on this forum that follow the events of Oblivion. Not all of them follow the main questline, but that's part of their creativity.
Acadian's http://www.gamesas.com/index.php?showtopic=1033100.
Rachel the Breton's http://www.gamesas.com/index.php?showtopic=1010914.
Bobg's http://www.gamesas.com/index.php?showtopic=862718.
Mirage in the Desert's http://www.gamesas.com/index.php?showtopic=860816.
FC4's http://www.gamesas.com/index.php?showtopic=854633 (technically, it follows the Shivering Isles questline)
My own http://www.gamesas.com/index.php?showtopic=859168 (eheh, plugging my own work
).
Really, just scan back through the fanfiction archives... maybe even do a search for "fanfiction" to help weed out the RPs. You'll find plenty of good stories here.