Bear mounts

Bears are the mainly ground mounts, that are obtained from a variety of different ways.

Purchased bears
While the rigging on the bears differs between Alliance and Horde, you are only offered your faction's version by Mei Francis in Dalaran. This will set you back, less any Kirin Tor reputation discount.

Achievement reward bears
Should you complete For The Alliance! or For The Horde!, the leader of your faction (Varian Wrynn for the alliance, Garrosh Hellscream for the Horde) will send you this mount. (You might want to avoid the postman for a few days...)

Loot bears
The Amani War Bear was a reward from Ashli's Bag for completing the timed event in Zul'Aman. When Wrath of the Lich King was released, this mount was removed from the rewards.

The White Polar Bear is found (very rarely) in the Hyldnir Spoils bag rewarded for completing one of several daily quests from Gretta the Arbiter in Brunnhildar Village.

Other bear mounts
The Big Battle Bear is a reward from turning in the code on one of the collectible game cards.

The Big Blizzard Bear was a reward from the BlizzCon 2008 welcome package (or from getting the DirectTV subscription in the USA).