One of the best overall introductory surveys related to issues surrounding GHG removal and the leading strategies to achieve it. You can request a copy from VEC by clicking on the link in the left column.
In 2007, Sir Richard Branson announced a $25 million innovation award for the first firm that can demonstrate technology able to remove 1 billion tons (a gigaton) of CO2 from the Earth's atmosphere. The VEC web site is a great resource for information about GHG removal and includes links to information about companies that are finalists for the award.
Some random articles
A good series of articles from the MIT Technology Review