Project Gutenberg has a mathematics section, and they prepare their more recent publications in a format that works very well on an ebook reader of moderate size: they generate PDFs in a size of $8.5\mathrm{in} \times 11\mathrm{in}$, with 12pt tex. They have some very interesting books.

I like this very much and therefore would like to know whether there are other websites that provide mathematical texts in this format.

Edit: After seeing the first answers I see that I had not explained clearly enough what I am asking for. I am not so much interested in mathematical PDFs in general, but in those that are optimised for small ebook readers. Most PDFs are made for printing, they consist of A4 pages with wide margins, and to read them comfortably I have to print them or by a larger ebook reader or tablet. The PDFs of Project Gutenberg have small margins, relatively large letters and a page ratio of approximately 5:4 and therefore display very well on a small ebook reader.

I have seen them until now only at Gutenberg, but would like to find other sources too.

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One thing you can theoretically do is download LaTeX/TeX source codes from arXiv and hack around with the preambles to make them compile in the A5(?) large-font marginless format you'd want to read on an e-reader. Unfortunately this is much easier said than done, and there is probably no automatic way to do that (although it might be a worthwile programming project to write some code that does it right in 50% of all cases). –  darij grinberg Jun 9 '13 at 21:14
@darij: actually, I've previously thought of using the TeX from arXiv for such and other interesting purposes! Maybe some CS student might enjoy this as a nice project... –  Suvrit Jun 9 '13 at 22:23
I have already thought of this; and with Gutenberg or arXiv files it is actually possible. It is however more than just changing the page size etc.; another point are the displayed equations, which often are too wide for a small text format and have to be rearranged. (But maybe the compilation to a landscape format would alleviate the problem.) –  rem Jun 10 '13 at 7:53
This is somewhat relevant: tex.stackexchange.com/questions/78920/… –  Neil Strickland Jun 10 '13 at 7:59

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It is not perhaps generally known that Wikipedia has a book creator, than can export any compilation of articles as PDFs. It is there on the left-hand sidebar:

http://en.wikipedia.org/w/index.php?title=Special:Book

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I use evopedia on my Onyx M92 and find it awesome. (only starting evopedia is a bit slow.) Slightly off topic, I can recommend the onyx m92 e-ink eader, my eyes are much more relaxed now. –  Martin Rubey Jun 9 '13 at 15:54

J.S. Milne creates some of his course notes in that format: http://www.jmilne.org/math/CourseNotes/index.html

If you are also interested in other ebook formats like EPUB, then you can search for books on http://www.libgen.org/ library, e.g. http://www.libgen.org/search.php?req=math+epub&nametype=orig&view=simple&column%5B%5D=title&column%5B%5D=author&column%5B%5D=series&column%5B%5D=periodical&column%5B%5D=publisher&column%5B%5D=extension

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The course notes by Milne are really nice. But I am quite a bit suspicious about the copyright status of the libgen files. Do I really have the right to download them? Otherwise, ebooks are certainly a good idea. –  rem Jun 10 '13 at 8:23

Well, this is perhaps as much a question as an answer, but for books about mathematics, it is reasonably likely that the original manuscript is in LaTeX, and it usually will be relatively easy to use the original input file and marry it with a different format file----

So "Does their exist a good pre-defined LaTeX ebook format?"

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This also works with the arXiv. With a small amount of effort you can (always?) download the source file and recompile it with margin changes. Now if someone were to write Firefox extension to do this... –  Jason Polak Jun 10 '13 at 1:48
There is no problem reformatting a LaTeX file for readers: remove the margins and decrease the amount of information on each page by changing the font size and the text area. The only problem, especially if formatting for a small device, is that many displays won't fit, and so have to be edited, which can take some work. With posted pdfs, you can use Acrobat to remove the margins, which helps, except that some sites password-protect their pdf files. –  anon Jun 10 '13 at 10:32

My terrible experience with Kindle is that diagrams are unrecoverably tiny and the lines are so faint that even with a mag glass you can't read them.

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Can't you zoom in? That's what I do. –  Deane Yang Jun 9 '13 at 23:15
Zooming only works (in the Kindle format, at least) on the text portion. It leaves diagrams tiny. In a book on category theory, this is problematic –  Carl Weisman Jun 10 '13 at 16:52