Books are where you find them, of course; but in my experience, most bookstores stock very little about space that will be useful to anyone who intends serious work around space settlements. Used-books stores and Campus bookstores are worth looking in to. It's good thinking to make a list of all resources that might be accessible to you. As you gain experience, summarize it into your space resources list. The best time to start this is now.
The two best suppliers of space settlements materials that I know of are Apogee and Univelt. My personal experience with both is good. Look for their huckster tables at annual space oriented events such as NSS ISDC and Mars Society. I base my following observations upon my own copies of the materials discussed and upon my own personal experience getting them. I purchased these materials of my own choice using my own dollars. For more information about the publishers, see their Web pages.
Apogee Books, http://www.apogeespacebooks.com/.
Apogee is Canadian but has a warehouse in America. They do more than books. Their Web site is very interesting to visit.
Recommended from Apogee for your library: their CD Orphans of Apollo. This CD documents a large story that "somehow" didn't reach the American news at the time, about the choice to destroy Russia's Mir space station. If you are working seriously at accomplishing space settlements, particularly out of America, you want to study this CD. Closely, in unhasty time; and remembering this quote from Adra's top page: "Think globally, act locally."
Studying this CD's story is a must if you expect to do any space settlements work; or even to publish relevant comments on today's news. Read between the lines in it to get vibes from very dark international and big-money politics. You will find much there to think upon. It's up to you to recognize practical meanings in that CD for yourself. (If you find none, you aren't doing anything. Review the quotes at Adra's top, choose a topic, and hop to it.)
We are touching some dark stuff here, and there's more. To find it, search on 'justiceforwalt' to find relevant cyberspace options. Watch for name 'Walter Anderson' in what comes up. The online Space Show wants your attention as a resource, and concerning this matter, go there and view, http://www.thespaceshow.com/detail.asp?q=708
(The above is hard stuff, and you want good tools to work it. See: epistemology, as a centrally important background and knowhow topic for anyone thinking about space settlements. You're going to want it here. If your epistemology is weak today (it's not a popular topic, but it should be), a good starting point is http://en.wikipedia.org/wiki/Epistemology. Start there now.
In a conversation at his display table in ISDC 2009, Richard Godwin mentioned to me that the CD, Orphans of Apollo, is available from Apogee priced $12 and $3 shipping. From Canada. A site he mentioned, 'justiceforwalt.com', seems not accessible from here.
After viewing Orphans of Apollo and while it's still fresh in your perceptions, you might want to fire up your favorite search engine and see what you can find out about the history and enforcement of Washington's ITAR regulations. And about what people working on space settlements have to say on this topic. (You may hear more said about ITAR at space oriented meetings than you'll see in print.)
Univelt Inc, http://www.univelt.com/
Univelt is publisher for the American Astronautical Society.
Recommended for your library from Univelt: Gary L. Harris, The Origins and Technology of the Advanced Extravehicular Space Suit. 2001. AAS History Series, Volume 24.
Owing to very slow space technology development in America, the book is usefully up to date despite its 2001 publication date. There are three strong reasons your library wants this book.
1) You don't see much in the news about space suits, but space suits technology is essential for any space settlements work. One of the very first tasks an off-Terra settlement must accomplish upon completing a basic lifespace and its local electric power resource, is a facility for space suits heavy maintenance and repair. This facility must develop quickly into an industrial base that makes space suits wholly from local materials. To place space suits in the general scheme of things, just imagine you're sitting in your off-Terra settlement -- and nobody can go outside. Human life off-Terra requires durable and inexpensive space suits with nearly the same priority as air and electric power.
2) A space suit is a miniature self-powered space station for a single occupant. To ready yourself for serious engineering and design work on space stations and settlements, start with space suit engineering. When you get around to larger projects, you'll want that tech and knowhow all over again.
3) Reading Harris, you'll soon find today's space suits are priced in the megabux range. This is much too pricey today for humans living in space. You can't afford to live in space if your space suit is priced at your 5-10 years income. Further, the numbers Harris provides on today's space suits service life, or for how many excursions out to space, will almost certainly surprise you. You thought you had enough challenge about human settlements in space? Add to your long list, reducing space suits costs by about 2-3 orders of magnitude while improving their useful lives by 1-2 orders of magnitude. (Here is a showstopper settlements challenge. Space suits. Who do you see working on it?)
Moon Miners Manifesto, http://www.moonsociety.org/chapters/milwaukee/mmm/.
Last in this short list but certainly not least is Moon Miners Manifesto. Its Moon Society location follows a move within the past few years, so if you are looking at archival materials do sort current from older. You want to look at Moon Miners Manifesto because it's a regular mine of information and thinking. (No pun intended here. MMM is really good.)
Which pulls in a related topic.
Adra is about settlements off-Terra, with strong hope (and little visible reality) in the prospect that someday America will realize some of its potential. To go out into space and place settlements there. There are basically four approaches to this, and as you read around you'll come across all of these:
1) Advance by slow degrees: build a new space station to replace or complement today's atmosphere-grazing ISS, but more far out. (The ISS wants frequent boosting to avoid Terran re-entry and burnup.) News published recently (2012 Feb) about such a space station, mentions the trojan outside Luna for that: fetch out fuels and depots to keep the fuels in, and etc. Develop from there. (Key point: such an orbital location is distant from all resources except solar energy. A good place to make fuels, if it had the needed raw materials.)
2) Luna settlement. Luna appears at first glance to be a superior location for a first settlement off-Terra. Upon more serious consideration, Luna has no atmosphere and a very hot origin with weak gravity; thus water and life chemicals are scarce there. (The goodies boiled off early that us humans would need.) Further, to land on Luna requires a large delta V; and another large delta V to leave it. Which greatly lowers Luna's value as a settlement and as a raw materials resource. (But its far side might be good for a radio telescope until large ones could be built in a Mars or Jupiter trojan.)
3) Mars settlement. Whoever says "Too far!" can prove his reality perception by a demonstration of crossing a chasm in two easy jumps. See Robert Zubrin's works and writings over the past three decades. Zubrin was right then and Zubrin is right now.
4) Asteroid mining and settlement. See Outland, a good video panned by Terran-oriented critics. Small delta V suffices to approach or leave an asteroid, and reason exists to believe that although time and water geological processes to concentrate ores could never have happened there, asteroids may even so offer valuable resources easily reached. Further, human life on an asteroid will be human life halfway to the Oort belt which in turn, approximates traveling by generation ship to nearby stars.