Abaddon's planet killer, any ship with Stage 2 Cyclonic Torpedoes, Some Ork Space Hulks if they build that Super Shokk Attack Gun one Mek did but that was more a case of mutual annihilation when the planet was teleported into the space hulk carrying it and both were destroyed. The Necron World Engine is probably capable of such a feat. A pair of Blackstone fortress could easily crack a planet, three were able to destroy a Star. A sufficiently potent C'tan or Greater Daemon could pull it off. The Tyranids may be able to literally tear one apart should they be pressed to the matter, they can take a noticeable chunk out of a planet but thats more of a "Why would they?" Ork Attack Moonz definitely could, since they could literally turn a star into a Black Hole. Thats honestly something I'd expect from Necrons, not Orks but stuff happens.
The Phalanx could perhaps accomplish this but it has not shown such a capacity.