Sometimes there is nothing better than swapping faces. The trick is to make it seamless. You know you've done a good job when the picture makes you laugh out loud, even after working on the image for 20 minutes.
Couple tricks to make the job easier:
When you grab a face, do a good bit of feathering. Always work in separate layers.
Watch your color balance. Blend each channel to match the face to the body.
Flip the image horizontally, as we see here. Most faces are looking a bit left or right.
This one's a great tip: When you're aligning the face, drop the transparency down so that you can see the original face underneath, along with the new face. This will help you get your alignment right in the eyes. The eye alignment is key.
When finished, chuckle and email all parties, or post on the internet (better!)