Superman Returns

Credit goes to the x360.org member that came up with this:

The Math: 10,000 tons = 20 million lbs aka 20,000,000

The heaviest item in the game is/are located at the Warworld chapter of the game, immediately after fighting the meteors at the begining of the game.

You are placed in an arene to fight some baddies, here you'll find buildings in the forms of "discs" stacked one on top of the other, these "discs" are 65,000lbs each and you'll find about 38 of them. Ignore the fight all together and start to pick these up and either A) throw them away, or my choice B) position yourself to let the missiles from the bad guy destroy the disc for you. With option B you can hover around and pick the next disc in the stack and rinse/repeat til the stack is finished, then move on to the next stack/building. Once done with all you'll probably have about 2.5million lbs. DO NOT QUIT, just let the guy defeat you and "retry", if you quit, you'll loose your progress.
How to get defeated fast? You get defeated by having your "crowd favorite" gauge at the top go all the way towards the picture of Superman. This will happen as the bad guy beats you down and depleats your stamina to knock you unconcious. To make go faster you can depleat it yourself by using superpowers which won't affect the bad guy anyways. This way the baddie will just have to hit you once to knock you out. It'll take 5 or 6 knockouts for you to loose

You'll need to do this eight times to gain 20 million lbs = 10,000 tons.

Option #2, if already well into the game is to visit one of the construction sites in the game and pick up/drop the I-Beams which will net you 11K lbs which will take FOREVER compared to the option above.

If playing through the game normally you will NEVER get even close to 10,000 tons. There are two good ways to get this achievement, but it will still take 1 to 2 hours to get.

1. At the beginning of the game you will be in Warworld, around the arena you will find huge chunks of rocks. These are the heaviest items in the game and can only be found here.
Simply pick it up, drop it, pick up, drop, rinse and repeat MANY times .

2. There are a few construction sites scattered around the city, here you will find metal construction beams, they are the second heaviest item in the game, simply pick one up, drop, pick up, drop it, rinse and repeat MANY times. Try doing it in a narrow alley or up against a wall so it doesn't go to far.

like everyone else is saying the discs are the best way to go for the achievement itself, but instead of one and letting it get destroyed its possible to cut the time of doing this achievement in half by catching them a few times in air before they break, if you can efficiently do 3-4 catches bam it brings that 2.5 mil a retry up to 6-8 or more depending on how many times you are able to juggle

This really sucks to get after you've left war world. One way to make it a little less terrible to is to head to the Research Park and look for the I-Beams as suggested. Grab one and head to the walled area they are near, line up several beams and toss them from inside the walled area. That way you don't have to worry about chasing them down if you accidentally stray too far from the wall with the wall/drop method.

The fastest way for me is the third(MONGUL)/last war world fight. If you try to go for the achievement on the first fight, the missiles will most likey break the (whole) disk before your able to lift it sometimes. second fight, the wave blast will knock you down. last fight will be the easiest and fastest way for this achievement in my eyes, let Mongul beat you, then you will spawn facing him and at your 11:00 o'clock position you will see one disk, fly to it before Mongul punches you, punch the blue support under the disk( this knocks the three supporting legs out the way the fastest ) And start picking up the disk while standing on the concrete slab and not on the same ground as mongul. doing this will allow you to do the most juggles without breaking the disk.