Someone was mentioning on #startups that there's a google code javascript plugin to do syntax highlighting and automatically detect the language, etc...
Personally, if all it does is put the code in a dark background and monospaced font that keeps the tabbing/spacing, that's already good enough for me! Syntax highlighting would really just be extra sugar.
I like that too. markdown@posterous.com -- that kind of change is going to take a little more than an hour's worth of work, though... might have to wait til morning.
Incidentally, there's another huge vote for Markdown from this corner---for me it kind of takes posterous from the toy column to the essential column. Which is not meant as a slight to posterous; I think it's the most elegant blogging system out there, bar none. But a lack of some kind of structured text means that I'd be having to hand-code html in a mail window. And I promised myself I'm never going back there... NEVER.
Can you put in pre tags as well? Many people set white-space: pre; for code tags in CSS, but other people actually use code tags within text to distinguish they are talking about the function or programming construct error, not a specific instance of an error.
I was thinking of just adding a [code] [/code] bbcode-like syntax for it, so you can totally still do it from email.
Otherwise if you're using the web editor in html mode you'll be able to throw <code></code> tags as usual to call into the CSS styles.
Definitely open to other suggestions too. =)