In the film and in prequel materiel, it is stated that Megatron crash landed on earth. That would mean he'd need to survive reentry and the subsequent impact on earth's surface.
Optimus Prime and Megatron both jump off a skyscraper and crash into one another in mid-air. Optimus Prime lands on his back to protect Sam, where as Megatron smashes head first into the street below. Both are temporarily incapacitated, but get back up and fight shortly thereafter. It should also be noted that they both hit the ground with sufficient force to deeply shatter the street around them.
Though Megatron clearly has the upper hand in the fight, Optimus Prime succeeds in landing several blows on him that actually cause the Decepticon to stagger backwards on two occasions. This is impressive because as I will eventually show, Optimus Prime is ludicrously strong.
And for the highlight of his durability feats in TF1. Megatron comes under fire from a squadron of F-22s, being hit with a total of 10 missiles along with dozens of other projectiles from soldiers on the ground. It was stated earlier in the film that Transformium melts at temperatures exceeding 6000 degrees. It was also stated that all military gunships would be retrofitted with incendiary ammunition to combat the Transformers. The grenade launchers used by the human soldiers also fire as Simmon states, "40mm sabot rounds". Despite this bombardment and his endurance wearing thin from constant battle, Megatron is still standing and does not appear to have much external damage save for leaking Energon.
Megatron finally meets his demise at the hands of the Allspark. Again, note how there is no visible damage from the bombardment he received moments ago. The melted metal on his hand/chest is from the Allspark.
Megatron's remains are dumped into the (second) deepest part of Earth's oceans, where no man-made vehicle is capable of entering without being crushed. Yet Megatron's body remains intact despite these extreme conditions:
A single bullet from Optimus Prime packs enough force to launch Megatron off his feet and through a building. Megatron is unharmed by either of these:
Optimus Prime bludgeons Megatron with a large tree (This one was hard to get a screenshot of, too much poop in the foreground):
Megatron is shot in the neck and head by an M1 Abrams tank. An M1 Abrams main cannon is chambered for a 105mm anti-tank cartridge. Megatron is mildly bothered by these.
Annd for the two highlights for ROTF. With the battle in egypt spiraling out of control, the US military decides to drop a 2000lbs JDAM, which is one of the most powerful explosive ordinances our military has.
Note how the entire area is engulfed by the bombardment, meaning there is no way Megatron was not hit. The blast wave alone knocks Ironhide and Sidesqwipe to the ground. And yet....
Megatron comes out of the smoke and flames unharmed then kills Sam, leading to part two:
Megatron is lit up by a squadron of tanks and soldiers carrying RPGs and Light Machine Guns. The machine guns don't do any damage, but Megatron successful withstands numerous shots from rockets and tank rounds before retreating.
Should Megatron's armor fail to protect him, he has shown incredible levels of endurance in the face of grievous injuries.
Optimus Prime dislocates Megatron's leg at the knee, whom doesn't really seem to be bothered. Moments later Megatron's leg is fine and he is able to walk normally.
This is the only highlight that comes to mind at the moment. Ill update the OP as I find more. Megatron is shot in the face with his own cannon, inflicting a horrific wound that destroys half his head:
Despite this Megatron immediately turns around to aim his weapon at Optimus only to have his arm severed...
And then sent flying several meters back and through a stone temple by Optimus's back cannons.
Resulting in the injuries you see here: