If you're desperate to tame a rare mob and you also happen to have a bit of money to spare, try transferring to a very low-population realm and camping there for a few days. I did this and got Skoll the moment I logged back in near one of his spawn points. On the third day before I transferred back, I found Skoll again. I wanted to tell someone, but Dalaran was barren at 4am and there wasn't a single hint of life in Storm Peaks. After literally half an hour of waiting to see if any hunters were around, I decided to kill Skoll with Skoll.
http://i20.photobucket.com/albums/b215/ ... _kill1.jpg
http://i20.photobucket.com/albums/b215/ ... kill1b.jpg
Of course I regret doing this now.

...But at the very least it shows how a temporary server switch can drastically increase your chances of taming that rare mob you've been after for months.
As a side note, I also managed to kill quite a few Northrend rare spawns while I was on the low-pop server. If I had stayed, I would've gotten the Frostbitten achievement in no time.
