Researchers at the University of Calgary say they have a machine that can extract carbon dioxide from the air at a reasonable cost and using relatively little energy. From what I can tell, the CO2 extracted would still need to be buried somewhere. Even so, if such technologies prove cost effective and scalable, they could potentially play a role in stabilizing climate.
More details are in this PDF. Apparently, the tower can capture 15 tonnes per year of CO2 per square metre and each tonne of capture requires 81 kilowatt-hours of electricity (about $4 worth). Estimated total costs per tonne (including capital) range between $12.80 and $43.80.