Denis at Heer46 has a cool little thing going with his 15mm tank and vehicle accessories. Right now he has several designs out for various German prototype tanks that were on the design blocks, but maybe due to resources or other reasons were not massed produced. These were the E-75 and E-100 series. The E-100s are much larger than even the King Tigers. With thick armor and massive guns. These would have been terrifying behemoths for allied tanks to go up against.
Since many of these designs are a little off from what Flames Of Wars folks have been used to seeing, they fit perfectly into a Weird War or alternate WWII setting. Check out and buy the Heer46 line or visit the Heer46 Blog