Other artifacts?
Sol Ring, of course. One land gets it out, which then gets your Millstone out. Turn 2, start milling.
http://magiccards.info/al/en/269.html
Icy Manipulator. Stall out some part of your opponent's deck.
http://magiccards.info/10e/en/326.html
Mishra's Helix as well. For the most part, he can't hurt you if he can't cast anything.
http://magiccards.info/us/en/302.html
As for non-artifact stuff to consider...
Blue is indeed the classic color for such a deck. With its counterspells and control cards, it lets you help lock your opponent while you mill him. Besides Braingeysers & the various counterspells, consider Capsize.
http://magiccards.info/fnmp/en/34.html
Black is another classic color, since its various discard cards are almost as effective in helping you lock a game down as blue is, and in addition, it gives you the additional threat of creature damage and direct damage. Some cards- Hypnotic Specter, Order of Yawgmoth, and Abyssal Specter- give you both discard AND creature damage at the same time. In addition, it gives you some land destruction.
Red gives you creature removal and direct damage, but also gives you land destruction unequalled in the game- if your opponents have no land, they probably can't cast too much, leaving you to Mill at whatever pace you want.
White has all kinds of annoying life gainers, creature removal/resets (Wrath of God, Cataclysm), and action-clogging cards (like Moat). Those all buy you time to Mill.
Green has virtually no support for this kind of build besides giving you creatures- giving you a mainstream damage threat that you can partner with Altar of Dementia and some of the other artifacts.
In addition, some special lands get you time or other threats. There are creature lands (Mishra's Factory), lands which damage (Desert) or stall out attacks (Ice Floe)- all of which give you time and flexibility.