Artificer's Spell Storing Item infusion really lets you make thingamabobs. The item stores any spell at 4th level or below for 1 hour/level. The Artificer thread mentions storing Speak with Dead in a dead body, or Charm Person in a gold coin for a super effective bribe. A few uses I've found, especially using the Spell Compendium, are spells that let you make a bridge that can hold 200 pounds/level, or Beget Bogun, giving you a little vegetable servant by storing the spell in the body you made for the spell. There are some other ones that give you a temporary flight or swim speed... That infusion really allows you to have the worlds largest bag of tools, with the only down sides being that it costs about 1 minute to cast, you get at most 4 casts of it per day without a sufficient intelligence modifier for bonus infusions, and it costs a small amount of XP.
I suppose this counts more as using obscure spells for utility, but combining it with specific items really makes for fun roleplaying.
