My novel includes excerpts of things like text from websites, tweets, and internet chats. I'm using Courier for the main novel font. Does switching to a san serif font make sense to represent the web stuff? It doesn't look good. Can you think of better ways to handle this?
I'd be inclined to just do a block indent for the web text. If it was pretty short, I might single space it, too, but if it's longer, I think I'd keep it double spaced. And I'd be consistent with that, so if you have ANY longer bits that you're going to want double spaced, I'd double space them all.
Web fonts are all over the place these days; I wouldn't stress that. As Kate S. said, block indent. I think you'll get a lot of mileage out of recognizable formatting and context hints, also:
This is a recognizable email format. Block-indented, it would be crystal-clear.
ErikRobson RT @Lynn If I use Twitter, I can tell right away that this is a tweet. (7 minutes ago)
Actual web site text is just... text. Usually nothing interesting about that. And, of course, forum posts have their own distinctive formatting, which varies across forum software.
I would also second Robusto's comment - not specifically for bad spelling and shortening, but it's worth noticing how people write across media. I've seen people who are perfectly capable writers but resort to shorthand and zero-punctuation when doing what they consider to be informal writing. Based on the online community, there are micro-dialects that community members use to fit in and identify each other. That's the sort of detail that I would be looking for from any Internet excerpts in a novel.
Definitely avoid sans-serif fronts in print, except perhaps for headings.
Indentation is probably the best idea, as others have suggested.
If you want to differentiate even more from other text, then perhaps try changing the font like this. Since your manuscript is written in Courier, then choose a serif font like Times New Roman for the emails, newspaper clippings, website etc.
That way, the change is quite noticeable, but not so distracting as to be unpleasant.
I wouldn't recommend using italics if they're long texts, because it could be tedious to read, plus you have the problem that, if you decide to use italics for a character's unspoken inner thoughts/thinking process, the reader may think you're referencing a quote from an email.
I am preferring to italicise "external sources" as thoughts, inner voices, memories, fragments from newspapers, books, letters, ... etc. I think it'd fit well to web fragments, too.