Infantry

Creeps
For times when you're too stingy to buy infantry. Level 2 and Level 3 creeps are darn good at breaking through outposts.

Boomer
Excellent against undefended artillery. Let these out near an enemy outpost and sadistically watch their outpost bulbs die. Use them behind tank lines when the tanks are busy shooting at something else.

Fixer

 * Send these little guys in groups! No fixer left behind! Squads of 4 are efficient; they will heal themselves as well as other units. Ideal against enemies who lack AOE damage abilites.

Creeper
Excellent against undefended artillery. Let these out near an enemy outpost and sadistically watch their outpost bulbs die. Use them behind tank lines when the tanks are busy shooting at something else.