http://forum.newsarama.com/showthread.php?t=99065 I think it's very cool. Tim Seeley from GIJoe has a cover image as well in the replies. The only one that bugs me is the McFarlane one. I mean look at it. It's the exact same pose as Spawn 1, 50, and 100 as well as the almost a mirror image of Spiderman 1. I know it's been a while Todd but really, something different would have been nice.
It's not. This is Spawn #1 flipped so that it'd match the direction Spider-Man's facing: #100 flipped: And it's not even anywhere near almost-a-mirror-image of this: People on other boards were thinking that McFarlane might've copied it from an earlier sketch he did (which is kinda believable) but still at best, you can say that it's slightly similar to Spawn #1, but it's most assuredly not exact.
Also http://www.wizarduniverse.com/magazine/wizard/003209582.cfm has images of Frank Cho's and JG Jones' covers up. Also, on the Liefeld board someone mentioned that Steve Ditko also contributed a cover, too (hasn't been shown yet; presumably they're keeping it a surprise for Los Angeles).