Everything I can think of...
1) Setting yourself up for a contingent Reincarnation using a wish and some sort of suicide ritual as a last extremity would probably work. Fails if your new form dies prior to being able to reset the system, but otherwise you'd live forever.
2) Put Clones of yourself in stasis/suspended animation, and arrange to have them wake up upon your death. Fails if you run out of Clones before you can reset the system, but otherwise you'd live forever.
3) Concerning your magic jar theory. Put your body in suspended animation after using a magic jar attack to leave it. Arrange to have it woken up if it is ever reoccupied. Cast majic jar from within your new body to keep changing bodies as needed. Works as long as your original body is not found, but there is a slight problem of aging a small amount every time you die violently and wake back up in your original body that you'd have to figure out eventually. Still, 1000's of years of this existence seems reasonable. I'm not sure if this works, but it sounds like it should. If not, your improved magic jar concept should work. The improved magic jar concept seems to be similar to 'The Strange Case of Charles Dexter Ward', and I wouldn't be surprised if there was a 2e Ravenloft Dark Lord with similar concept.
4) Find a way to create and consume a Potion of Youth every few years. Fails if you die a violent death, but staves off old age indefinately. I'm pretty sure the potion exists in earlier editions of D&D - not sure if it is officially in 3e or later.
5) Transform yourself permenently by ritual or wish into a form that doesn't age. Fails if you die a violent death, but otherwise you live forever. Note that for most campaign worlds, becoming a diety falls into this class - deity being only limited protection from violent deaths. Note, depending on your reading of say Greek Myth, it's possible that the Greek dieites actually belong in category #4 above, if in fact they would age if it where not for their continual consumption of Ambrosia.
6) Take one or more Epic feats that makes you ageless regardless of form. Fails if you die a violent death, but easily within the reach of any sufficiently powerful character.
7) In certain settings, it seems like it is possible to place your life/soul either temporarily or permentently in a physical object without becoming a lich. I think Voldemort from Harry Potter is best understood as being a sort of Undead in that setting, but in Neverwhere by Neil Gaimen one of the character's places his life temporarily in a different object and thereby causes his body to able to be rejuvinated/reginerated by returning his life to it. He does this without apparantly being undead, but he does require assistance to ensure that his body and life are reunited. Effectively this is like raising yourself. It's not clear that this protects from old age unless you also become undead however, there is the example of the priest whose 'heart is not in it' from I3 Pyramid. On the other hand, I converted him to 3e as a greater mummy...
7a) In Planescape:Torment, the protagonist seems to have arranged a rather complex and more foolproof variation of the above, the details I won't go into in order to avoid spoilers.
8) You mention Fistandantilius, but you don't mention Beren who seems to be absolutely indestructible in the form of the Green Stone Man. It's not at all clear how you'd arrange to end up in that condition though, as it seems to entirely involve a very non-gamist power of plot assertion. It's worth noting that Harry Potter's condition seems to be rather similar however, with his Mother rather than Sister in the role of the animating/protecting power. I'm not sure whether you'd want to introduce that pattern to your campaign though.
