Derek Allard has a quick post for the CodeIgniter users out there with some styling you can use on the default CI calendar.
A project I'm working on needs a monthly calendar. Naturally, I'm using CodeIgniter as the base of it. [...] My needs were something more akin to the interface iCal provides; broad, spacious, subtle. Obviously, the default is just an unstyled base that CI provides as a starting grounds. The Calendar library documentation provides some insight into how we can start changing this up.
He talks about the settings he needed to change including the "day_type" setting and template that specifies the CSS classes to use. Add in the CSS and you'll end up with something like this. You can download the example files too.