Weighing in at 30,000 pounds, the Massive Ordnance Penetrator of the US Air Force will become the largest air-dropped non-nuclear bomb ever built:
http://www.popsci.com/military-aviation-amp-space/article/2009-08/pentagon-wants-deploy-largest-non-nuclear-bomb-next-year
The MOP is 20 feet long and can penetrate bunkers up to 200 feet before exploding. At 15 tons, the MOP is a third heavier than the previous "mother of all bombs", the GBU-43/B Massive Ordnance Air Blast bomb, which was only 10.5 tons. The MOP also packs a whopping 5,300 lbs of explosives, which is 10 times the amount its predecessor bunker-buster, the BLU-109, carried. Basically, it's massive.
The push for accelerated deployment is due to the increased perceived nuclear threats from Iran and North Korea. It's believed that many of their nuclear programs could be in development underground, below levels of current bunker-busting bombs' range. The Pentagon intends the rapid deployment to send a message that the United States is tweaking strategies to address new threats. And nothing is more American than advertising the sheer size and tonnage of the bombs hanging below our jets.
http://www.popsci.com/military-aviation-amp-space/article/2009-08/pentagon-wants-deploy-largest-non-nuclear-bomb-next-year
Thanks, America!
Foreigner1 is right - it's part of a spread of available tools and would be chosen to play a particular role. It's not the be-all and end-all of everything - just as no other weapon has been over the years. Vastly powerful fusion weapons once appeared to be the end of weapons development. For a while no one could see beyond them. As it turns out they were probably something of a dead end.
What would be really nice would be to spend some of the money doing something rather more useful. Like being nice to people.