Tinkering is a Tradeskill that allows players to create fireworks, and other mechanical goods. A skill only known to Gnomes, tinkerers can make fun and exotic goods, some with stat bonuses. Since only gnomes can train it to its true potential, it can be a fun tradeskill to level and use.
Gnomes are have a natural bonus to intelligence. Increasing the tinkering skill should be easiest for intelligence casters.