I know that you guys are into character pieces and not bouncing balls anymore, but squash and stretch can be applied to many other situations besides cartoony balls, such as walks, faces (here and here) and in this case a jump. Plus I just wanted to post those images because they're awesome.
Another thing worth pointing out for those who will or want to do a jump. Don't forget to fully extend the legs (or whatever the character uses... arms?) during the lift off and to extend the limbs before the touchdown as well (unless there is a specific reason for NOT doing it).
Images found via Haha.nu @ ejphoto