The Resurrection Stone, one of the Deathly Hallows, represents the desire to bring back the dead. More specifically, it represents the danger of that desire when pushed to the point of actually trying to resurrect the dead. Dumbledore ruined his hand and eventually brought about his own death by trying to use it to speak with his parents and sister, and the brother in the Hallows story found himself drawn to suicide after using the Stone. This danger is further symbolized by the fact that it is cracked, that it is cursed (having been one of Voldemort’s Horcruxes), and that it appeared on the ring of the wicked Marvolo Gaunt.
The Elder Wand, the first of the three Hallows, is a wand that ensures that its master will win any duel. No one can truly possess it without defeating its former owner. Since defeating the owner in a duel is impossible, this feat is always accomplished by stealth, murder, or surprise attack. Thus, the Wand symbolizes both the thirst for unbridled power and the folly of believing that power and violence can keep you safe. From the first possessor of the wand onward, the wand has brought death to those who owned it.
The locket Horcrux that Harry and his friends recover from Umbridge is, like all of the Horcruxes, cursed. It tries to kill Harry by strangling him when he’s underwater, it burns itself into his flesh when he’s fighting Nagini, and it keeps him from summoning his Patronus by exerting an almost imperceptible negative influence on the emotions of those who wear it. Nevertheless, its main function in the plot is not as a magical item or one that can act to produce serious consequences. Instead, it seems to symbolize whatever is within each of the characters that they have to overcome within themselves. With Ron, it helps exacerbate his discomfort and childishness until he abandons Harry. When Umbridge has it on, it brings out her own characteristic flaw—her penchant for lying.