Hella Supertone Horn Set # 3AG 003 399-801  The kit comes with a separate relay which I used.  The stock horn wiring activates the relay. 

You can see the red horns through the grill.  I mounted them in the same spot as the factory horns.  These Hella horns are a lot louder than the stock 1999 horns but still have that import sound.  I personally think the stock 2002 4Runner horns are the best.  They have a hearty American sound to them.