You can also get what is one of the best looking land mounts in the game by simply grinding Wintersaber Trainers rep in Winterspring. You need to get to exalted by doing 3 quests over-and-over.
It took me a little while to get mine.
Here's a pic of one:
http://i.thottbot.com/ss/s/1019.jpg
Another mount you can get in 1 evening is by completing the achievement [For the Alliance] whereby you kill all 4 leaders of the horde cities. Blizzard then mails you a Black war bear. As long as you parttake in the fights it doesn't matter which level you are - granted it will be pretty tough for anyone below lvl 78 to get there - even in a raid of 40 strong.
http://img75.imageshack.us/img75/7818/00000blackwarbearyy8.jpg
Very rare drops include:
The Zulian tiger & Raptor from Zul Gurrub,
Midnight from killing Attumen in Karazhan,
The warsteed from killing the Baron,
The brewfest kudu from killing the brewmaster,
I can't remember the others off hand.