http://www.astrobio.net/debates/6/terraforming-debate
10 essays/arguments written by different scientists having a debate and pointing out important considerations in regards to Terraforming.

http://www.users.globalnet.co.uk/~mfogg/index.htm
The personal website (looks atrocious) of one of the foremost experts on Terraforming, M.J Fogg. Contains several of his published essays on the topic, as well as list of works which might prove useful.

Useful links from above website:
http://www.users.globalnet.co.uk/~mfogg/paper1.htm (Review of research)
http://www.users.globalnet.co.uk/~mfogg/biblio.htm (Bibliography)
http://www.users.globalnet.co.uk/~mfogg/zubrin.htm (Tech Requirements)

http://espace.library.uq.edu.au/view/UQ:158029
The ethics of space colonization and terraforming

http://conservancy.umn.edu/bitstream/92791/1/Schmidt_umn_0130E_11135.pdf
Phd thesis on the real possibilities of Terraforming

http://strathprints.strath.ac.uk/15099/
Proposal on using solar reflectors to increase the surface temperature of Mars enough to melt the ice and make it more habitable.

Really useful as it shows loads of technologies as well as when we can expect them. Each of the items has a linked source for it, so although the original site my not be citable, you can still get citations from it.

http://www.Stirlingengine.com/faq - An organization dedicated to educating the public on Stirling technology and its benefits.

http://www.howstuffworks.com/stirling-engine.htm - A step by step explanation of the basic principals at work in Stirling engines.

http://www.ohio.edu/mechanical/Stirling/engines/engines.html - A more detailed look at the physics and exact implementation of Stirling engines.

http://mac6.ma.psu.edu/stirling/reports/19970012689_1997021349.pdf - The report of NASA/MTI's research into automotive Stirling engines.