The best Snytax Highlighter to use is:
You just insert the following below in your theme:
<link rel="stylesheet" href="/path/to/styles/default.css">
and then use <pre> tags for your code and that is it!
The Snytax Highlighter auto detects the language the code is, so you don't have to specify C# or HTML
it does all of it for you.
Even works when you multiple languages in the same page.
On top of that you have 20+ themes to choice from:
You can have a Visual Studio, GitHub, Google Code, School Book, and etc to choice from, lots of different options for themes.
It is also very light code wise so not much of a resource load.