There's one really easy and striking effect you can achieve in PhotoShop. The effect puts forward a part of your image by leaving it colored versus to the uncolored background. As with many effects it can be reached through various paths. Here's one of them.

1. Create a copy of a background layer and make a selection of an object with any of Photoshop tools or plug-ins (I used Extract)

2. Load a selection (if you used a plug-in)

3. In the menu choose Select>Inverse

4. In the menu again go to Image>Adjustment>Hue/Saturation. Reduce Saturation to minimum 

5.Go to Select>Deselect (Ctrl+D). Your object is now standing out.

6. To make this image into a greeting card I chose to add an inscription to it by using Horizontal Type tool.