In Marvel's Civil War, Wolverine and Sentry came to blows as the most powerful character in the Marvel Universe realized that even with godlike power, he couldn't kill the X-Men's resident brawler. Instead, Bob Reynolds admitted to Logan that while he couldn't end his life due to his mutant healing factor, he could make him feel pain on a level that few could dole out - and Sentry delivered.
Sentry is the most absurdly powered hero in Marvel Comics, as he's essentially a reality-warper who has decided to switch between being Superman and the devil. As a hero, he's got the powers of a million exploding suns, with a wide checklist of abilities that make him practically unstoppable. However, when Sentry gained his powers through an experimental Super-Soldier Serum, he also bonded with the Void, a living darkness capable of destroying the entire universe. So, while Sentry's powers don't have an upper limit, the Void makes him dangerous and unpredictable - Sentry even conspired to wipe his existence from the minds of everyone on Earth (twice) so the Void couldn't manifest. But, unfortunately, it didn't stick, and Sentry and Void have reappeared many times since.
In Wolverine #47 by Marc Guggenheim, Humberto Ramos, Carlos Cuevas, Edgar Delgado, and VC's Randy Gentile, Wolverine and the Sentry found themselves on opposite sides of the Superhero Registration Act. Wolverine fought against the accord, while Sentry helped SHIELD track down those who opposed it. In the issue, Sentry confronts Wolverine, telling him to stand down against the forces trying to bring him in for defying the act. However, Wolverine doesn't back off, leading Sentry to punch him so hard, Logan admits his opponent "hits like friggin' Galactus."
Sentry admits he doesn't think he can overcome Wolverine's healing factor to put him down for good, but that it won't stop him from feeling pain. Wolverine tries to fight back, but Sentry grabs his claws and starts pushing them into his hands before delivering a mammoth punch that knocks the mutant out cold. Wolverine awakens in SHIELD custody, making it clear that Sentry's mission was successful.
Wolverine's healing factor had Sentry, Marvel's most powerful hero, admitting he was unkillable. While that clearly doesn't make Logan unbeatable, it's a true badge of honor, and shows just how impossible it is to put Logan down for good. Recent comics have seen Wolverine admit that he often throws himself into combat as a distraction, knowing he'll be badly injured as the first wave, but confident he can take it in order to set his allies up for the win. What some might see as masochism or even foolishess is borne out by Sentry admitting that even his incredible power isn't enough to kill Logan. While he lost this particular fight, Wolverine's healing factor was put to the test facing a foe like Sentry, and it passed with flying colors.