I'm a big fan of complete victory with little risk, so I tend to like the weaves that aren't as limited as fireballs and explosions and tend to pure lethality. I'm a big fan of the weave the Black Ajah Yellow Sister used to destroy the bones and organs of the Panarch, for example.

Intoxication=A simple weave of Water and Earth that causes the victim to exhibit the symptoms of extreme intoxication. There is nothing better than making an enemy fall down drunk when they are in the middle of a speech or a pitched battle.
Poison Spray=Use Water, Air, Earth and Fire to create an area where oxygen is turned into gases that are lethal to beings that need to breathe O2. Can be sent as a cloud that will travel until dispersed by the wind or projected in a sphere around the channeler or in a single direction.
Directed Whirlpool=Use flows of Water to create a whirlpool in a body of water, and then either move it onto land where the flows will keep it as a mass of directed fluid or use it to sink ships. Would have been perfect to defeat the Seanchan when the Seafolk went against them.
Hail Storm=Use flows of Water and Air to create missiles of super-hardened moisture that fall from the sky with enough force to break bones and damage structures.
Paralysis=Spirit, Water and Fire are used to make the victims nerves go numb, and inhibiting the electrical impulses between their synapses.