Django -- Can't get static CSS files to load

I'm running Django's development server (runserver) on my local machine (Mac OS X) and cannot get the CSS files to load.

Here are the relevant entries in settings.py:

STATIC_ROOT = '/Users/username/Projects/mysite/static/'

STATIC_URL = '/static/'

STATICFILES_DIRS = (
'/Users/thaymore/Projects/mysite/cal/static',
)

STATICFILES_FINDERS = (
'django.contrib.staticfiles.finders.FileSystemFinder',
'django.contrib.staticfiles.finders.AppDirectoriesFinder',
#'django.contrib.staticfiles.finders.DefaultStorageFinder',
)

INSTALLED_APPS = (
# other apps ...
'django.contrib.staticfiles',
)

In my views.py I'm requesting the context:

return render_to_response("cal/main.html",dict(entries=entries),context_instance=RequestContext(request))

And in my template the {{ STATIC_URL }} renders correctly:

<link type="text/css" href="{{ STATIC_URL }}css/main.css" />

Turns into:

<link type="text/css" href="/static/css/main.css"/>

Which is where the file is actually located. I also ran collectstatic to make sure all the files were collected.

I also have the following lines in my urls.py:

from django.contrib.staticfiles.urls import staticfiles_urlpatterns

urlpatterns += staticfiles_urlpatterns()

I'm new to Django so am probably missing something simple -- would appreciate any help.