I just found this out, and i’m sure a lot of people probably already knew this, but as always, I’m late the game. Anyway, WordPress.com has built in support for source code highlighting. I’ve already updated several of my posts to use it. Here’s the link showing how
http://en.support.wordpress.com/code/posting-source-code/
The TL;DR of it is you just put the following around the code in your post:
[sourcecode language="css"]
your code here
[/sourcecode]
Filling in the language with whatever your posting in. The list of supported languages on the link I posted above is pretty short but I get the impression it’s probably not been updated in a while either.
Try entering source code. Then go to the Visual Editor then back to Text editor. Tell me how that works for you.