A couple of days ago I posted a link to a free, open-source, textbook (Introduction to Sociology), the open-availability of which made me think about whether there were any other sociology books lying around in some dusty corner of the web just waiting to be found, dusted-down and presented to a wider audience.
And the answer, since you’re currently reading this post, is that clearly there was. I’ve managed to uncover 7 such texts that should be of at least some interest to a-level Sociology students and teachers. There are, however, a few things it might be useful to point out:
1. The texts I’ve listed aren’t the very latest versions in a series. While I’ve tried not to include very old editions (there’s nothing from the last century…) if you want the most up-to-date versions you’re going to have to buy them.
2. Most of the texts are from American publishers. They reflect American Sociological Specifications and preoccupations and invariably draw much of their illustrative material from American society. While this is not necessary A Bad Thing (depending, of course, on your view of Americentricity) it does mean you’re not going to find many references to non-American examples and illustrations. You’ll also find that data about areas like crime, marriage, education and so forth is pretty-much wholly-focused on North America. While this may be useful for comparative purposes you need to be careful students don’t assume such data necessarily reflects the situation in other countries around the world.
3. Following from the above, these texts are not likely to fit neatly with, for example, UK A-level Sociology Specifications. You will, however, find a lot of the content is universal: theories of crime commonly discussed in UK textbooks, for example, are also likely to be discussed in American textbooks.
Textbooks
1. Sociology for Dummies (2010): If 
you want to give your students a slightly irreverent take on sociology and sociologists this can be a good place to start. Although it’s not a textbook, as such, it does contain a lot of useful material. More importantly, however, encouraging your students to read any “non-textbook sociology” resource is probably a bonus.
2. Sociology 101: Another fairly recent text that conforms, once again, to contemporary notions of textbook design. It does, however, have quite a bit of text packed into its pages and this probably reflects the fact it’s mainly aimed at American undergraduate Introduction to Sociology (Sociology 101) courses. Having said that there’s little here that should be beyond most a-level students. Once again you’ll find familiar sections (Family, Education, Deviance…) sitting alongside sections (Politics and the Economy, Urbanisation) that don’t really feature much in UK Specifications.
3. Sociology in Our Times (2012): This is a contemporary-styled textbook and the areas it covers (family, education, deviance, religion…) will be familiar to UK Sociology teachers and students, as will much of the content.
4. Introduction to Sociology (2012): This is a more conventional sociology textbook from Wikibooks built around the Wikipedia “open content” principle that it can be edited by anyone – something that’s both a towering strength and obvious potential weakness. You can download the pdf version of the book or, if you prefer, simply view it online (which will give you some idea of both content and general format). As a general rule it’s text-heavy and picture-light.
5. Basics of Sociology (2005): Although a slightly older text that makes few, if any, concessions to contemporary styling (when I say it’s a text book I really mean it’s a book with lots of text). In this respect it’s a bit like the “Themes and Perspectives” produced around this time – perhaps a little advanced for many students but may reward those who like to read about things in a little more depth.
6. Sociology: Brief Edition (2012): Another perfectly-serviceable American textbook, released under a Creative Commons licence. It’s probably a little more text-heavy than more contemporary texts but once again it’s a book whose general content could be used to give your students a bit more depth if you think they need it.
All of the documents here are in pdf format so if you only want to use some pages from a document you can use a pdf editor. If you need a free one, a selection are reviewed here.