As stated on the home-page, this is not a total guide to all research materials available, but is worthwhile in terms of pointing you (9/11 believers, critics and the curious alike) towards sources performing the following functions, in general (but not exclusively) from perspectives that are either critical of the 9/11 cult, or agnostic on the subject--in other words merely outlining facts/events without conspiracy theories in mind.  Our list is necessarily selective.  We aim to:
1) Draw attention to the deep background to 9/11, particularly the origins and nature of Al Qaeda, seen from various angles.
2) Look at the technical/narrative details of what actually happened on 9/11
3) Comment on the activities and especially arguments of the 9/11 Truth cult in broader perspective. 
Where relevant, web-based resources will be cited, but a curse of the internet is that for many, if something is not on the internet, or was pre-internet, it is discounted in various ways.  Especially remiss concerning a topic where many interesting first-hand memoirs have been written, that only fleetingly, like comets, impinge on the consciousness of net-heads.   This page will be updated and extended as time goes by--suggestions welcome.  The use of three red asterisks after a source below (***) indicates that for legal reasons it is difficult/impossible to get in the UK: US booksellers are useful here.  A majority of these books (all as far as we know) seem to have been stamped on, using the UK's libel laws/the threat of them.  In every case so far, the litigious parties are powerful Saudis.  For reasons that will be obvious if you read them--even if such elementary logic has eluded the razor-blunt minds of 9/11 cultists.   
Nafeez Mosaddeq Ahmed 'The War on Freedom:How & Why America was Attacked 11/9/01' Tree of Life Joshua Tree California (2002) ISBN 0-930852-40-0: an important early work, placing 9/11 properly within the context of US foreign policy.  While drawing negative inferences about the lack of an adequate US military response before/on 9/11, a world away from loony-tune rubbish about pods/holograms etc. 
Nafeez Mosaddeq Ahmed 'Subverting 'Terrorism'--Muslim Problem or Covert Operations Nightmare? Institute For Policy Development & Research Working Paper London (2006): carefully argued and meticulously referenced attempt to locate Al Qaeda as a Saudi/US construct.  Doesn't quite prove his case about Al Qaeda representing a global 'strategy of tension', but worthy of detailed study
Abdel Bari Atwan 'The Secret History of Al-Qaida'  Saqi Books London (2006) ISBN 0-86356-760-6: while weak on the subterranean links between Al-Qaeda and the CIA etc, captures well enough the reality and self-image of the network
Jean-Charles Brisard & Guillaume Dasquie 'Forbidden Truth: US-Taliban Secret Oil Diplomacy and the Failed Hunt for Bin Laden' Thunders Mouth Press/Nation Books New York (2002)  ISBN 1-56025-414-9: written by authors with extensive contacts in French intelligence, this fascinating book explores in substantiated detail the close relationship between the US government, spooks, the Taliban & Bin Laden.  Along the way some key documents, including CIA/FBI & State Department files on Bin Laden are reproduced.  As too the first ever arrest warrant on him (prompted by LIbya).  Essential source. ***

Jason Burke 'Al Qaeda: the true story of Radical Islam' Penguin London (2004) ISBN 0-141-01912-3: a mixed bag.  On the one hand, very weak on original links between Al Qaeda & the CIA, for example.  On the other, good in explaining how Al Qaeda is now a franchise, or idea, as much as solid network.  In that sense, the banner can be (is) taken up by many with no formal connection to Bin Laden/his lieutenants.
Steve Coll 'Ghost Wars--the Secret History of the CIA, Afghanistan & Bin Laden, From the Soviet Invasion to September 10 2001'  Penguin London (2004) ISBN 0-141-02080-6: all the complex detail missing from Burke (for example) on this topic.  Particularly good on the complex politics of Pakistan & Afghanistan, rightly placing the latter country at the forefront of understanding Al Qaeda
John K Cooley 'Unholy Wars: Afghanistan, America & International Terrorism' Pluto London (1999) ISBN 0-7453-1328-0: another essential source, all the more so in that Cooley outlines the woeful consequences of US covert foreign policy, in alliance with the Saudis, before 9/11 itself.  Hence, he cannot be accused of merely being wise after the event.
Peter Dale Scott '9/11 in Historical Perspective: Flawed Assumptions': Briefing for US Congressional Staff (2005): concise (perhaps overly so) attempt to remind decision-makers of US role in Al Qaeda creation
Robert Dreyfuss 'Devils Game: How the US Helped Unleash Fundamentalist Islam' Metropolitan Books New York (2005) ISBN 0-8050-7652-2: absolutely essential background text, showing with chapter and verse how for many years the US helped prop up/sponsor 'Islamic Militancy'.  This is important not just to confound simplistic jihadist propaganda (of Bin Laden's sort) but also to explain the historical context within which 'blowback' (a la 9/11) becomes perfectly comprehensible.  A book to make everybody uncomfortable!
Rachel Ehrenfeld 'Funding Evil:How Terrorism is Financed--and How to Stop it'  Bonus Books Chicago (2005)  ISBN 1-56625-231-8: aspects of this book are almost cartoonish in their politically illiterate stereotyping.  However...it struck a raw nerve with the Saudis for disclosing 'intelligence insider' material (foreword by R James Woolsey ex-CIA Director after all).  Some grains of wheat among the chaff. ***
Yosri Fouda & Nick Fielding 'Masterminds of Terror' Mainstream Edinburgh (2003) ISBN 1-84018-724-7
some fascinating background material on the Al Qaeda operatives Ramzi Binalshibh and Khaild Shaikh Mohammed involved in planning 9/11 & creating the broader network.
Bruce Lawrence (ed) 'Messages to the World: the Statements of Osama Bin Laden' Verso London (2005) ISBN 1-84467-045-7: another essential text, explaining Bin Laden's world view from his own mouth, and along the way ('Towers of Lebanon' 29/10/04) claiming Al Qaeda responsibility for 9/11.
John Miller & Michael Stone 'The Cell--Inside the 9/11 Plot & why the FBI & CIA Failed to Stop It' Hyperion New York (2003) ISBN 0-7868-8782-6: a standard, but nonetheless informative, inside track account of the obstacles placed in the way of those investigating Al Qaeda activities in the US.
Michael Moore 'The Official Fahrenheit 9/11 Reader' Penguin London (2004) ISBN 0-141-02138-1: the book of the film that catalysed interest in 9/11 for many.  Despite its populist style, makes some useful points about the Saudi: Bush connection--presumably why the fruitloops now view Moore himself with suspicion
'Rebuilding Americas Defenses' Project For a New American Century Washington DC (2000): as important for what it doesn't say as it does.  Imperialist strategy--certainly, and brutal in places.  But a text advocating a 'New Pearl Harbour', as Griffin et al. claim? Not at all (see p.51)
Mohamed Sifaoui 'Inside Al Qaeda' Granta London (2003) ISBN 1-86207-682-0: an interesting first person account from an Algerian journalist who infiltrated Al Qaeda's European network.  An important corrective to fantasists deluded enough to believe such didn't/doesn't exist.
Craig Unger 'House of Bush: House of Saud' Gibson Square London (2005) ISBN 1903933625: superb and vital text on the murky relationship between the Bush dynasty and the Saudis--and how this facilitated the construction of Al Qaeda.  Far too empirical for conspiracy theorists   ***
Lawrence Wright 'The Looming Tower: Al Qaeda's Road to 9/11' Penguin London (2006) ISBN 0-713-99973-X: fascinating detail on many of the key players both from Al Qaeda and their antagonists, such as the tragic John O'Neill of the FBI.  Some useful theorising on inter-agency rivalry too.