My favourite weapon enhancements are the Transmuting and Morphing enhancements.

Transmuting changes the type of metal the weapon is made out of, to morph to beat the DR of whatever you just hit it with, if possible.

Morphing lets you change the weapon between, say, a greatsword and a glaive.

My artificier greatly enjoys the use of it. Really suits the adaptable role of the character in his party.