So, I spent last month deciding to go have fun in cata 5-man heroics. Yes, you can actually solo cata 5-man Heroic instances. Gear + good strategy is enough for the major part.
Now, I checked internet and youtube, so if I made an error, please tell me :)
So, as far as worldfirst are concerned, I did:
Ulthok not very hard, just positioning and moving quickly.
Foe reaper 5000: Trivial
Springvale: Good thing I discovered the glitch on ashbury :)
Ammunae: also called the technical strategy boss, since timings are on a very narrow window, so you have to deal with adds, interuupts, loss of focus, and still dps the boss.
Setesh: complementary to ammunae, he's not technical, he's about reacting to chaos
Augh: lots of doubt for this one, I don't see why a dk hasn't solo'd him before, so maybe not a worldfirst.
Corborus: run, little dwarf, run!
Nalorakk: hah, that was a hell of a boss to solo! Pet health was limit, hunter health too, and dps too! Great boss to check the mist changes when they will be active.
Malacrass: free loot :)
Now, for Hunter worldfirsts:
Ashbury: first cata boss I tried, first challenge, learned a few things :) Also discovered the leaving combat glitch (that, I believe, doesn't work against raid bosses).
Helix : Fun boss, since you have 0.5 seconds to click on intervene when he yells.
Anraphet: the bug hits again... but he's got a water warden, so it's thanks to him that HoO isn't soloable :)
Rajh: easy easy easy
Throngus: now this is real soloing! Fun fun fun :)
Now, which bosses haven't been solo'd yet by a hunter? For those seeking an extra challenge, here is the list! Note that I haven't gone farther than zul'aman, so I can't give advice for ZG/4.3
In green, those who could be possible in heroic DS gear (my opinion)
Mindbender gur'sha: you need to tank him, and he hits hard (hunter survival)
Ascendant lord obsidius: nasty DoT (hunter survival)
Dragha shadowburner: shadow bolts (hunter survival)
Erudax: need lots of dps
Akil'zon: massive damage on hunter (hunter survival)
Halazzi: Massive damage on pet, self-healing... there could be a strategy to kill him.
Drakaara: Massive damage in lynx phase (bear is impossible) (hunter/pet survival)
Edge of madness
Echo of Baine
Echo of Sylvanas
All hour of twilight
All well of eternity