Only problem I have with using a Plug-in for this, is that most tend to be insecure, like fckeditor which is highly popular(and outdated on most sites from users who upgrade wordpress, but not their plug-ins), that allows file upload vulns.

If a plugin is insecure and has upload vulnerabilities, PLEASE report that to plugins AT Wordpress DOT org ASAP. We will review and close it.

Meanwhile, if you check out CSS editor, which was added to Jetpack, it looks like folks are experimenting with syntax highlighting and line numbering in the CSS editor there, so maybe we'll get that soon.

Only problem I have with using a Plug-in for this, is that most tend to be insecure, like fckeditor which is highly popular(and outdated on most sites from users who upgrade wordpress, but not their plug-ins), that allows file upload vulns.

In all honesty, shouldn't be too hard to add to the core of WordPress, if plug-in authors are doing it already. I would feel much safer with a built in core function, knowing the code was scrutinized a bit more, and that bug fixes would come with every new WordPress release. Not to mention having the ability to maybe toggle it via the post/page editor, like one of the little icons above the post editor for visual editing, having one for HTML syntax highlighting with the ability to turn it on and off also makes sense, since not everyone will want to have it on all the time.

By the way, this should be not only in the post/page editor, it should also be in the plug-in and theme editor sections as well, since PHP syntax highlighting would make so much more sense with line numbering to track errors as well.

http://wordpress.org/extend/plugins/wp-editor/

Try Synchi...
http://wordpress.org/extend/plugins/synchi/

Regards.

Is there a plugin to do this?

Implement Syntax highlighting to HTML part of post editor