Some good K3 plots here, here's mine:
You play an ex-Jedi Padawan who was about 13 years old, who escaped during the destruction of the acedemy in KotOR I. You were given refuge and hidden from the Sith by a kind married couple who were farmers on a remote area of Dantooine.
You soon became detached from the life of a Jedi after years of farming, however, now 18 years old, suddenly you feel an overwhelming urge to seek the fate of the Jedi. You hear of the events on Telos and decide to head off an seek what remains of the Jedi Order.
Among the ruins of the Jedi academy you come across a man calling himself the 'Desciple'. He tells you what happens during K2, specifically at Malachor. Intriguied by his tales, you team up with him and head off to Telos, where Desciple introduces you to Carth & Bastila.
They tell you of the great threat from the 'true Sith' and ask you aid the Republic by scouting the Unknown Regoins for any trace of the Exile & Revan.
With Bastila as a mentor you build a lightsaber and slowly re-gain your affinity with the force. You set off on you travels with mostly new party members, some old ones too.
Don't have time to write this in more detail at the moment (gotta go to work! :<), maybe someone else wants to continue it.
Anyway thats my suggestion.