Weapon Advancement

[Olethros]

Does anybody know of any weapons that by RAW continue to get better as the user gains lvls. Specifically I am looking for more than a few level dependent effects, but actually continue to be usefull to the user at increasing lvls either by new abilities being added, additional hit bonuses, etc.

I realise that homebrewing something like this wouldn't be hard, but I was allways curious if D&D had something already printed.

[Fax Celestis]

The book you need is Weapons of Legacy.

[PinkysBrain]

Weapons of Legacy, although most prefab weapons aren't really worth it (too many non-scaling abilities which become useless at higher levels).

[AmberVael]

Alternately, you can go for the Unearthed Arcana stuff, though Weapons of Legacy is probably much better.
Legendary Weapons from UA
Item familiars from UA

[Clementx]

Ancestral Weapon from BoED (requires good, not Exalted, luckily) lets you pray your loot into magic bonuses- 50% more efficient than actually paying sensible market prices.

[Rahdjan]

Kensai PrC from CW.

[Amphimir Míriel]

I was about to mention the Samurai from Oriental Adventures... but I'd rather not mention that sad, sad class

[fallensavior]

Yes. You get gp. Then you pay a wizard to make your magic weapon of +1 more. Your fine as long as you keep getting gp.