This is for the level 50 rare elite crocolisk pet in Stormwind.
First we must head to Stormwind, this is a realitivly easy pet to get for Alliance, but rather difficult for Horde. Once in Stormwind, head to coords (8758x473) to generalize the instance street, seen in this screenshot here
once you are where I stand, turn directly around and you will see a small house entrance with steps leading up. Face the water channel, and in first person mode slowly back up to this spot here untill Stormwind disappears, you should be able to see under Stormwind, now look to your left and you should see the "Sewer Beast" seen in this screenshot here . He is a 50 elite. All you have to do is lay the frost trap, and open attack, lead him onto the frost trap and boom, congratulations on your croc!
*Edit*
The only way that you cannot capture a beast is if you use "Beast Lore" and it says "Cannot be tamed". This Beast is captureable, one of my friends has tested it. This pet is really nice, can tank like a mother and has a lot of HP and Armor. Another nice thing about it is it sticks low to the ground so viewing over the pet isn't an issue.
*Edit* (again)
I also have a level 36 Orc Hunter and I have the rare elite pet "The Rake" . You can find and tame him in Mulgore.
*edit*
OK, the only difference between a non-elite pet and an elite pet is damage, armor, and stats. Most mobs that are non-elite plain suck for hunter pets. If you tame an elite, damage is better, armor is better and so are all stats. If you are lucky enough to tame a rare elite, then you have even more bonuses to stats, armor, etc. *NOTE* If you don't know what the hell you are talking about e.g. if you've never played a hunter please don't say stuff about pet capturing, if you have a question I understand.