Anyway, hivemind's blog posts aside I narrowed down the remaining 'worthwhile' legendaries I need that would be useful from Classic and GvG:
Class:
Tiron - In every Paladin deck but Eboladin. Will probably be in every Paladin deck save extreme aggro FO'EVAH.
Antonidas - Seems to be in every Mage deck... including Mech Mage now. Can't see it ever falling out of use.
Al'Akir - In maybe a little over half the Shaman decks I see. It's a solid card but not in the Tirion/Antonidas tier as far as effects, imo.
Cenarius - Good but I'm missing the key Druid epics so it's pointless.
Neptulon - A good value card but I haven't seen it used in many decks for a while now.
Vol'jin - Seems to be in most Priest decks but mostly a glorified removal. I'd probably prefer Paletress for RNG wackiness.
Jaraxxus - Don't really see it much anymore.
Mal'ganis - Has apparently taken Jaraxxus' place even though they do different things.
Neutral:
Thalnos - A good card but only used in Freeze Mage (which I don't like), some Rogue decks, and some Druid decks.
Legendaries that would be cool to have for gimmick decks but ones I'd probably never craft: Deathwing, Hogger, Cairne, Leeroy, Tinkmaster, Mukla, Van Cleef, Gallywix, and maybe Toshley.