http://braveandboldlost.blogspot.com/
A fun site that falls squarely into the "What-If" realm. The site's creator uses MS Paint (the masochist) for all his covers and continues to get better with the compositing. He started with "The Brave and the Bold" and now continues with "Marvel Two in One" covers.
Enjoy!
I can show you the result of one of those covers:
http://www.artofjohnbyrne.com/gallery/commissions/crossovers/Batman.Wolverine_copy.jpg.php
(And no, I don't own that piece of art, unfortunately.)