In the Ultimates I loved it when the Hulk was having trouble killing that one alien/german dude (I can't believe I don't remember his name). No matter what the Hulk did the guy just kept regenerating himself so the Hulk eats the guy. The on image that stands out is the hulk eating the guys head.That just figgin genius. Then they had to run test on the gamma active stool samples from the Hulk.
Solomon Grundy's death in Starman was pretty touching. Just as he hooks you as a lovable oaf he saves Jack Knight and co. from being crushed under a mall, says he's sorry for all his past incarnations' wrongdoings with a tear in his eye, then collapses under the wreckage. It's probably pretty cliche but it tugged at my heartstrings.