PowerPoint gives you immense power and freedom to use your imagination, creativity to create a great greeting card for any occasion. With typical greeting card websites it's way difficult to pick the correct card which can express your deep emotions. Animations, sound, your own narration in PowerPoint will help you ponder your inner emotions in a PowerPoint slide show in a much better way.
So just build up a theme or story and start creating your own very special card. Get some cool pictures, templates, music or record narration if you want to send more personalized card. Make sure to time it with cool animations and transitions.
Image via Wikipedia
Why not create your own Halloween greeting card, full of bats, jack-o'-lantern, ghosts, skeletons, witches, devils and some scary music. Have a look on Halloween cards on Slideshare and authorSTREAM, read Microsoft's step by step guide on How to Create a multimedia greeting card in PowerPoint and get started.
Update: authorSTREAM already has a greeting card section which has user submitted presentation cards for different events and festivals. Either you can use greeting cards available on authorSTREAM or upload your own PowerPoint presentation, add some background theme, message and share it with your loved ones.