I've found some good and bad legendary stuff. I play on Survival, so I can't take two steps without running into Legendary Feral Mongrel #27. Here are the good ones, that I wear and use:
Wounding Laser Musket (targets bleed for 25 points of damage, cutting right through the absurd damage resistance they have on Survival difficulty)
+AP Regeneration Metal arm (doesn't say how much, but makes quite a difference)
+50% Robot damage 10mm pistol (turret-shredder and synth-buster)
And here are some of the many, many bad ones:
Enraging Rolling Pin - critical hits cause target to frenzy
Poisoner's Leather Armor - 25 poison resistance is good, leather armor is bad
Irradiating laser musket - would have been good on a bullet-spraying weapon, useless on a powerful one-shotter