It is common simply to use italics. I don't know that there are or are not any 'established rules' or where they might be found but different (online) publications seem to use different treatments without causing confusion, to me anyway. I have seen titles in bold, in "quotes" and in italics and in bold italics.

Wikipedia uses italics as does the (US) Library of Congress.

Thank you very much for your quick answer. Much appreciated.

I don't know that there are or are not any 'established rules'

Oh, there are absolutely established rules--the Chicago Manual of Style [chicagomanualofstyle.org] comes to mind. (Italicized because that is an actual title of a book.)

Now, if this question had been posed in the HTML subforum we could have talked about the new markups in HTML5.
:: shuffling papers ::
It’s called <cite> [html.spec.whatwg.org], an inline element. Further research reveals that its default formatting is, as you might expect, italic.

Edit: Oh, wait, I assumed on no particular grounds that the question was about the title of a book. Italics are used for books, plays, films, operas and the like--any complete independent work. Songs and poems go in quotation marks instead. Unless, sigh, it’s a book-length poem. The Iliad vs. “Trees”, say. Names of seafaring vessels are also italicized, regardless of size. (It would admittedly be fun if ocean liners were italicized while rowboats were in quotes :) )

There are writing rules for print publications (Chicago Manual of Styles, [chicagomanualofstyle.org...] ) which show how titles of publications, movies, articles, works of art, music, stage, etc are to be treated. If nothing else, this manual does provide a very consistent formatting process for English based "written" communications. I suspect there are others out there, but this is the one I have used for a zillion years.

Thank you everybody for all your interesting and useful answers!