Custom tag for post-source

Hello,

A simple question I think:

Is there a way to add a custom field for the source of a post, next to ‘written by’ and date etc.?

If you want to know what I mean, just check http://frontpage.fok.nl/ and just click on a new post on the left sidebar. In that post you see the source (in dutch source is ‘Bron’) and the website link to the source.
And that’s what I want for my website at http://www.klifix.nl/

I hope someone can help me out, I’m looking for such a thing for a long time and tried several plugins that didn’t exactly do what I mean.

Thanx in advance!