if u ask to list useful legendaries the list would be much shorter to read.

weapons - echoing fury, skorn, manticore
helm - mempo
shoulder - vileward
chest - IK, inna's, tal rasha's..tyrael might is nice too if 2 socket
bracers - lacuni's
glove - tasker theo
belts - witching hour
pants - blackthorne's, inna's or depth digger
boots - ice climber, IK, Inna's or Natalya's
ammy - tal rasha's..but usually rare trifecta are better
rings - hellfire's, natalya's, wailing host, zuni's pox

that's my list..

np..although some legends is useful depends on build..like 300th spear for range barb..but what I listed is just in general..as opposed to maybe 5x of the amount of useless legendaries lol..hopefully the item patch will fix this problem