Intrigued by this fairly detailed explanation of what a Green Lantern movie starring Jack Black would have been like, I looked around for concept art and discovered that David Boreanaz was once considered for the lead. I also found a Jack Black as Green Lantern paper toy for download. The illustration you see above is via.
The other what if of the day is Christina Hendricks as Wonder Woman. I couldn't find any decent images imagining that (link is NSFW).