Blinkmoth Nexus

{T}: Add {C}.
{1}: Blinkmoth Nexus becomes a 1/1 Blinkmoth artifact creature with flying until end of turn. It's still a land.
{1}, {T}: Target Blinkmoth creature gets +1/+1 until end of turn.

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.

Etched Champion

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

Arcbound Ravager

Sacrifice an artifact: Put a +1/+1 counter on Arcbound Ravager.
Modular 1 (This creature enters with a +1/+1 counter on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

Cranial Plating

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

Mox Opal

Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.

Memnite

Springleaf Drum

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

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.)

Spire of Industry

{T}: Add {C}.
{T}, Pay 1 life: Add one mana of any color. Activate only if you control an artifact.

Steel Overseer

{T}: Put a +1/+1 counter on each artifact creature you control.

Darksteel Citadel

Mountain

Master of Etherium

Master of Etherium's power and toughness are each equal to the number of artifacts you control.
Other artifact creatures you control get +1/+1.

Inkmoth Nexus

{T}: Add {C}.
{1}: Inkmoth Nexus becomes a 1/1 Phyrexian Blinkmoth artifact creature with flying and infect until end of turn. It's still a land. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Island

Ornithopter

Galvanic Blast

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