Sorry, no real links as such as it was a good while ago when I used to make greeting cards. Search Google for pre-scored blank greeting cards. I used to do mainly A4 that folded to A5.
If you have a cutter that uses a mat then you can produce cards that are a cut above (pun intended!). You can cut contoured edges that match your print, or scalloped edgez, or lace effect, whatever.
You really need pre-scored cards though, or a scoring tool and board for a professional fold.