[Taqwus]

There are also a few melee weapons with an area effect. Ember, the Stone Sword, Sun Slayer, the Sword of Many Colours come to mind, perhaps others. There's also one blade -- Harvest Blade? -- which automatically hits and cripples all units in a square, if memory serves.
But otherwise... load up on Boots of Quickness or the Jade Armor, or use area-effect spells.