Elvis, of course, loved his mama Gladys. In fact, his love for his mom may be the reason he first set foot in a recording studio - the story goes that he wanted to record a very belated birthday present for Gladys and went to Sun Records' Memphis Recording Service to lay down a couple of songs for her - "My Happiness" and "That's When Your Heartaches Begin." Gladys was obsessed with her son, probably with good reason - as most people know, his twin brother was stillborn and Gladys was unable to have children after that, so Elvis was all she had. She walked him to school and he rubbed her feet; she later lived with him at Graceland until her death in 1958. Rumor even has it that they slept in the same bed until he was in his teens, which really would be no surprise - Elvis grew up in a two-room shack.
Photo from Random House
Douglas MacArthur was the youngest of three sons and apparently his mom didn't want to deal with empty nest syndrome when he left for the United States Military Academy at West Point: she camped out in a hotel room overlooking the Academy grounds for two years. Supposedly she even bought a telescope so she could make sure he was studying instead of getting up to shenanigans, but that smells like an urban legend to me. But one book does say that he met with his mother for at least half an hour every night after dinner, and if he couldn't get away, she would meet him so they could walk and talk on school grounds instead.
Photo from the Smithsonian
Franklin Delano Roosevelt
You'd have to be a pretty formidable women to intimidate Eleanor Roosevelt, and FDR's mom Sara was just that. Franklin was her only child (I'm sensing a trend here) and she was quite protective of him. She even homeschooled him until he went to boarding school, and when he was admitted to Harvard she followed him there. She was upset when Franklin got engaged to Eleanor, but when he got married against her wishes, she committed herself to controlling both of them. Sara picked out the newly-married couple's first house, had it decorated, and bought herself a house just three blocks away. In 1908 she gave them a townhouse in Manhattan which conveniently connected to her own townhouse - it had adjoining doors on every single floor. Franklin later admitted he had been terrified of his mother his whole life.
Photo from the National Park Service
Liberace, like Elvis, had a twin who died at birth. He was devoted to his mother, and it showed: one newspaper described him as "a deadly, winking, sniggering, snuggling, chromium-plated, scent-impregnated, luminous, quivering, giggling, fruit-flavored, mincing, ice-covered heap of mother love." He talked about her so much in his act that she became "Mother" to his fans as well; when she had a heart attack his fans flooded her hospital room and house with flowers and cards and well wishes. But like Franklin, it turns out that Liberace was actually quite scared of mommy dearest: when she died in 1980, he confessed, "I'm finally free." He was well into his 60s at the time.
Photo from the Sacramento Bee
Surprise, surprise. As his mother's firstborn, he was her "Golden Siggie" and she very obviously played favorites, even giving him his own room and making her other children share. She doted on him to the point that he started to experience sexual desire for her (hey, he documented it!) and wished he could get rid of his father and have his mother entirely to himself. According to Freud, a wise old woman had told his mother that her firstborn son was going to do great things, so her adoration of him may have had something to do with that.
Robert E. Howard
Perhaps the biggest mama's boy of all, for quite disturbing reasons. Robert Howard was a playwright and an author who created the character of Conan the Barbarian. His mother, Hester, was a particularly selfless woman who was passionate about instilling a love for literature and the arts in her children. She was known for caring for sick friends and relatives to fault - it was because of this compassion that she caught tuberculosis and fell extremely ill. She was in poor health for the rest of his life. Howard himself suffered from bouts of extreme depression; he was talking about suicide as early as his teens. He told friends the only thing keeping him from killing himself was his obligation to his poor mother, who wouldn't be able to cope with such an ending. Despite his writing success, when his mother slipped into a coma in 1936 and her nurse told him she would never open her eyes again, he saw his chance. He went immediately to his car, took a gun from the glove compartment and shot himself in the head. He died eight hours later and his mother died the next day.