The Gnomish Army Knife is quite possibly one of the greatest creations for crafters and gatherers.  It reduces over various profession-related items into one and is usable by non-engineers!

Can act as:
Gyromatic Micro-Adjuster
Arclight Spanner
Flint and Tinder (which no longer needs simple wood to make fire)
Blacksmithing Hammer
Mining Pick
Skinning Knife
Jumper Cables (engineers only)

These knives are good for lvling engineering, so they should be cheap on the AH.  Enjoy!

Edit: tidied up the link

-- Edited by Monk at 14:56, 2009-01-23