Vertus Play With Pictures ($40, 15-day free trial) is appropriately named. This standalone program gives you comparatively easy-to use-tools for cutting out portions of your photographs to put into a new background. For instance, you can take a self-portrait at work, and put yourself on the beach in Hawaii. Then, you can add a tall fruit drink into your hands, slap on some text, and put in a speech bubble to taunt your friends when you e-mail it out.
Play With Pictures is based on the same masking engine as Vertus's professional Fluid Mask, so it generally does a good job. But it works best if you use pictures with good contrast on the edges. (Professional photographers will typically plan their shoots, using contrasting background--the traditional "blue screen" method--when they know they will want to put their subject into a different background.)
The interface is clean and easy to understand, with simple navigation. The Play With Pictures Website has excellent video tutorials that will get you up and playing quickly. Play With Pictures works by automatically analyzing your picture, to figure out what might be the background and what is the subject you want to keep. But you can edit those outlined areas, redefining the edges. The touch-up brush even does a nice job with fuzzy fur or flyaway hair (if there is enough contrast for it to work on). When you are satisfied, click a button, and your cutout will be put into the new background. Not satisfied with the edges? You can re-edit the cutout. The Save options are limited to JPG or PNG files, or you can print out your collage.
Play With Pictures doesn't take itself very seriously. It's simply a fun consumer-level program that hobbyist photographers will enjoy.