Additional blog settings

Is there any way to add settings to WordPress?

I’m trying to run a bunch of sites that use the same template but I want to be able to add additional settings to each blog that aren’t covered by the standard settings.

Is there some sort of custom attribute plugin for the blog itself (not for posts). I think such a feature would be very useful.

An example would be defining the logo URL for the blog. Or including some custom CSS.

I want to be able to use these settings in the template.

I like how pages/posts have custom attributes. Anything possible for the blog itself?