Lands:
Scorched Ruins: $2.46: If your meta is light on land destruction, this land is great ramp.
Eldrazi Temple: 40c - $1.00: Excellent addition considering all of the Eldrazi coming out.

Utility:
Shimmer Myr: $1.12: Helps equalize the playing field by letting you cast spells at instant speed like the rest of the table
Citanul Flute: $1.28: Having experimented with Aladdin's Lamp, I find this to be an overall upgrade. For the same amount of mana as the Lamp, this lets you cast it and search for a 5-drop.

Political:
Spectral Searchlight: 16c: Giving someone a mana that they need in a pinch definitely puts you on their good side.

Control:
Lodestone Golem: 50c: Slows down the competition

Defense:
Witchbane Orb: 75c: Since you are an artifact deck with no counterspells (until BfZ maybe?) this can help protect you from spells which target players.
Portcullis: 40c: Prevents the board from being flooded with creatures. Especially useful against token decks and decks that go wide.
General's Regalia: 32c: redirects all of that pesky damage to an indestructible creature.
Silent Arbiter: 92c: Helps slow down creature combat if you are lacking in board presence early on.

Ramp:
Blinkmoth Urn: $1:35: One of the best ways to ramp in an artifact deck but can make you a target at the table.

Combo:
Krark-Clan Ironworks: $3.40: Lets you sac your thoptors and weenies. Also gives you a sac outlet for combos.
Nim-Deathmantle: $1.95: Another combo piece but can also save your creatures.
Su-Chi: $4.00: The last combo piece which can give you infinite mana along with Nim-Deathmantle & a sac outlet like Krark. It also combos well with a sac outlet which makes your opponent mill.
Voltaic Construct: 25c: A nice combo piece that synergizes with Karn + Dreamstone Hedron or any other artifact that makes 3 or more mana. This will yield infinite mana. With Karn & Planar Portal, it will let you play your entire deck.
Voltaic Key: 50c: So many uses. Mana ramp, resets a blocker, use your favorite artifact twice...
Unwinding Clock: $4.21: The most pricey artifact here but it's value is incredible.

Recursion:
Elixir of Immortality: 34c: Life and lets you Planar Portal & Flute for stuff that's already gone to the graveyard.

Super fun but might make people punch you.
Worldslayer! 34c: For all of your worldslaying needs...
Spawnsire of Ulamog: $3.23: Depending on your meta's opinion about EDH sideboarding, this card plus tons/infinite mana = fun for the whole table.