I have been made aware of a link to an Excel document listing all of the e-books purchased by the University on a librarians' website, which I thought might be useful for anyone who just wants to browse through a list of them, organised by subject: http://www.lib.cam.ac.uk/libraries/ebooks_coll.html
But of course there is plenty of information on e-books on the ebooks@cambridge website here: http://www.lib.cam.ac.uk/ebooks/ It allows you to search for e-books and also provides links to all the collections that have been purchased. There is also comprehensive help in using e-books, information on how to use e-books on mobile devices, how to cite e-books, and a list of free e-books widely available on the web.
Don't forget also to check out the eReference section linking to the amazing Oxford Reference Online collection of online subject and language dictionaries and thesauri, and all the other reference e-books purchased by the university, such as Who's Who.
In general, you can use the online catalogue LibrarySearch to find e-books at http://www.lib.cam.ac.uk/newton/ The book titles have '[electronic resource]' next to them. You will be able to click on this and go through to the e-book (and if you're away from the university you will be prompted to enter your Raven password to access the e-book).
We've also put handy little stickers on the covers of printed books that are also available online, with a link to the online catalogue so you can access it!