I'd like to offer our syntax highlighter library highlight.js for using on the Stack Exchange sites. I am perfectly aware that you already have one in place and there was a similar discussion a while ago, so the burden is on me to explain why you might want to even bother :-)
What's in it for Stack Overflow
Better lexing. Correct lexing and parsing is kind of our holy cow. For example we don't confuse regexes with division in CoffeeScript, are able to distinguish method definitions and method calls in Java, know 10 different variants of string syntax in Ruby, etc. I'm not saying we're 100% correct but I do believe we're better at it than any other client-side solution.
Better language detection. Here's one example of a mishighlighted code that we correctly detect and highlight as CSS. I actually used to routinely visit Stack Overflow and test our language detection on every code fragment that I stumble upon. Fixed a lot of bugs :-).
More languages. The raw number right now is 103 though quite a few of them a rather obscure. Still, we tend to get support for new and hot languages pretty quickly. Go, Swift, CoffeeScript, F#, Groovy, Scala, etc.
The most important thing: we actively work on the project and we have a good development process. Detection tests, markup tests, Travis builds, quick painless releases and a lot of work going into fixing bugs.
What's in it for us
In a word, exposure.
I never actively marketed the library and we got to the point where we have an excellent product but not enough people knowing about it. We have quite a few small and medium-sized sites that use the library but to go further we need someone bigger.
Better exposure also means better exposure of bugs which we could fix and make the library better. I noticed that people using the library on their blogs tend to not report bugs at all and simply ignore them. On Stack Overflow we could even create a custom bug report button to submit mis-highlighted code to our site.
Are you interested?
P.S. Sorry for the possibly awkward language, I'm not used to giving "sales pitches" :-)