NestaCMS - A Ruby CMS for developers and designers. With simple code that's easy to follow, Nesta is easily extended using the Sinatra web framework.
I recently went through setting up syntax highlighting on Nesta for this site. I started with "Setting up rack-codehighlighter" from the Nesta site, but wasn't loving what Coderay had to offer. Looking at 'rack-codehighlighter' and it's other formatter options and decided to use Ultraviolet.
While this is geared towards Nesta, this will also work for all Rack applications, especially those built on Sinatra.