If the original poster is looking for a Hallmark or American Greeting type program, none of these are suitable replacements. These greeting card apps (my wife loves them) come with a bunch of premade cards, you select a card from the list and print it. It does let you edit the cards (or create one from scratch) but my wife never does more with it than personalize the card (and I suspect most that use these things do the same).
Unfortunately the only app available for OS X that I've found is Print Explosion Deluxe. Comparing it to Hallmark (what my wife has used for the past 4-5 years) it has less cards and is considerably harder to use. It is also very unstable. She finds it very frustrating to use (the way she edits cards seems to induce instability into the app) and she is isn't computer literate enough to realize that when it starts acting flakey it's time shut it down and restart. I made a few cards in it for her and you can pick out a card and personalize it, after that your best bet is to restart it after you do one card as it rarely stays stable through making a second. The biggest instability culprint appears to be dragging and sizing objects on the card; it corrupts the internal object model and you start getting missing objects, extra junk objects, or crashes.
I ended up installing an XP VM on her Mac so she can use the Hallmark program.