I love the ambivalent apology offered in these Sew Dandee cards. They proclaim simply, "I assume I f*cked up in some way, so I'm sorry." I mean, what more surefire way can you think of to have your beloved forgive you for your screw-up than a card like this? I'm for it.
These Sew Dandee cards need to be in everyone's drawer for that catch-all, cure-all remedy. They come in a variety of colors, too--see the link on the left for more.