Galvanic Blast

Galvanic Blast deals 2 damage to any target.
Metalcraft — Galvanic Blast deals 4 damage instead if you control three or more artifacts.

Memnite

Swamp

Cranial Plating

Equipped creature gets +1/+0 for each artifact you control.
{B}{B}: Attach Cranial Plating to target creature you control.
Equip {1}

Whipflare

Whipflare deals 2 damage to each nonartifact creature.

Ornithopter

Island

Shivan Reef

{T}: Add {C}.
{T}: Add {U} or {R}. Shivan Reef deals 1 damage to you.

Vault Skirge

({B/P} can be paid with either {B} or 2 life.)
Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Springleaf Drum

{T}, Tap an untapped creature you control: Add one mana of any color.

Thoughtcast

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Draw two cards.

Signal Pest

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
Signal Pest can't be blocked except by creatures with flying or reach.

Chief of the Foundry

Other artifact creatures you control get +1/+1.

Shrapnel Blast

As an additional cost to cast this spell, sacrifice an artifact.
Shrapnel Blast deals 5 damage to any target.

Darksteel Citadel

Mana Leak

Counter target spell unless its controller pays {3}.

Etched Champion

Metalcraft — Etched Champion has protection from each color as long as you control three or more artifacts.