Here's an awesome series of variant cover art for Marvel NOW! created by Charles Paul Wilson III. As you will see they all pay tribute to the legendary art work of Jack Kirby. I've included Kirby's original work for comparison.
Then there's this one. The original art wasn't from Kirby, but it's still a fun variant that I thought I'd throw into the mix as a bonus. The original cover art for this on was done by Rob Liefeld.