This is not a definitive list but is the one that i use the most frequently as it a) gives me access to books and also b) it gives me a view of where tech is going. In general publishers are there to make money, so they print books that will sell and so their lists tend to reflect trends in programming and computer science and usage. I say in general because some of the list are historical and some are self publishing sites which are therefore open to anyone.
Words of warning. There will always be bad books. Badly written, full of proprietary libraries and code, written by self delusional authors, copies of the documentation that has been released by a project etc. So read reviews, check on Amazon to see that people say there, use the look inside facility many site offer to read a few pages online to get a feel for what is there.
The list. In no particular order and i am not specifically recommending one publisher over another.
O’Reilly — Large and well established company with a good reputation especially in the open source area. However they also cover the “proprietary” areas such as Microsoft, Cisco, Oracle etc. Mainly publishes technical books. For a long period O’Reilly book covers depicted animals to the extent that the Perl books with a Camel on the front simply became known as the “Camel” book
Pragmatic Publishers - “The Pragmatic Programmers is a company with a simple goal: to improve the lives of developers. We create timely, practical books, audio books and videos on classic and cutting-edge topics to help you learn and practice your craft. Our titles do not contain any Digital Restrictions Management, and have always been DRM-free; we pioneered the “beta book” concept; we’ll email your ebook to your Kindle and synch your ebooks amongst your devices via Dropbox, and you can re-download your purchases at any time. We’re here to make your life easier.“Smaller publisher but, and this is a personal opinion, strikes me as more the haute coture of tech publishing than O’Reilly’s Asda. Don’t get me wrong i love OR and probably have more of thier books than anyone, but a new Prag Pub book is always a delight to me. They also have a monthly magazine which is worth a read.If anything Prag lean towards the Java/Groovy/Scala/Erlang school of publishing but have iOS titles as well as more general ones.
Wrox - Wrox were early into the publishing scene for tech books concentrating on Microsoft related titles and then branching out into open source titles. They always had, and i believe still do, programmers writing the books. In 2003 they became insolvent (think dot com bust) and were taken over by Wiley. Distinctive for their solid red covers
Manning - Founded in 1990 and concentrating on science and engineering but steadily moving into computing and the internet. Manning cover use old lithographs of costume worn by people 150 to 200 years ago (and mainly living in the Balkans it seems to me)
Packt - Comment to follow
Apress - Comment to follow
Effendi - Comment to follow
Addison Wesley/Pearson - Comment to follow
Informit - Comment to follow