This is something I've been keeping track of for a long time now in Northrend. Outland works by the same system also, but i am yet to bring this to the old world because the idea is daunting because of the lack of flying mounts, and i don't speed hack.
Now Everyone knows that rare spawns have seemingly random spawn timers, though you hear the 6 hour interval get thrown around a lot.
What i have discovered is that both of these are correct.
Rare spawns in each continent(not yet confirmed for old world) have a 6 hour SHARED spawn time.
So what we do, is log on as soon as the servers come up from maintenance or a reset or a wold server crash and kill the first 4 100% confirmed rare spawns that will always be there after servers come back up.
These are Perobas the bloodthirster, Vigdis the warmaiden, Icehorn and Greigan. I'll attatch some maps of all rare locations also.
(on oceanic servers time) 5.30 ish will also get you King Ping.
Now after you kill the first 4 rare spawns (5 if close to king pings spawn time) record the times of death and in 6 hours time go for a fly around to the other locations to find yourself some more rares to kill (or bodies).
This can also be used to help you track TLPD as he shares a spawn with Vyragosa, if you have the times that rares will spawn, then start each flight around searching for rares with Vyragosa's spawn point.
I have gotten TLPD from this, and i have all but 2 of the rare spawns (lokeh'quan [slept something like this] and Aotona) bacause they are highly saught after as hunter pets.
No an easy macro to use to find rares everywhere in northrend is this:
/tar Ao
/tar Dirk
/tar Grie
/tar High Thane Jo
/tar Icehor
/tar King
/tar Old C
/tar Putridu
/tar Seet
/tar Terr
/tar Vigd
/tar Crazed I
/tar Fum
/tar Groc
/tar Hild
/tar Loq
/tar Pero
/tar Syr
/tar Tuk
/tar Vyr
/tar Zul'drak S
/tar Scarlet Hi
/tar Time
that has all rares names in it and fits under the 255 cap
Howling Fjord - http://i46.photobucket.com/albums/f1...rdrareszf1.jpg
Grizzly Hills - http://i46.photobucket.com/albums/f1...rarespawns.png
Dragonblight - http://i46.photobucket.com/albums/f1...rarespawns.png
Borean Tundra - http://i46.photobucket.com/albums/f1...rarespawns.png
Scholazar Basin - http://i46.photobucket.com/albums/f1...rarespawns.png
Icecrown - http://i46.photobucket.com/albums/f1...aresmapyw6.jpg
Storm Peaks - http://i46.photobucket.com/albums/f1...aresmapje6.jpg
Zul’Drak - http://i46.photobucket.com/albums/f1...rarespawns.png
and this macro for outland
/tar Fulgor
/tar Mekt
/tar Vorak
/tar Martic
/tar Bog Lurk
/tar Coilfang Em
/tar Crip
/tar Doomsay
/tar Okrek
/tar Goretoo
/tar Voidhunt
/tar Morc
/tar Hema
/tar Speak
/tar Nura
/tar Ever-Core
/tar Chief Engineer L
/tar Collid
/tar Kraat
/tar Ambassador J
Hellfire - http://i46.photobucket.com/albums/f1...rarespawns.jpg
Zangamarsh - http://i46.photobucket.com/albums/f1...rarespawns.png
Terokkar - http://i46.photobucket.com/albums/f1...rarespawns.jpg
Nagrand - http://i46.photobucket.com/albums/f1...rarespawns.png
BEM - http://i46.photobucket.com/albums/f1...rarespawns.jpg
Netherstorm - http://i46.photobucket.com/albums/f1...rarespawns.jpg
SMV - http://i46.photobucket.com/albums/f1...rarespawns.jpg