Geez too numerous to mention, lol.

Most memorable I suppose would be a Hyacinth parrot for less than 100g twice and reposted it for several K. This was before thye made them epic drops - so people are more aware they have something special now.

Pets all the time. Especially the Argent pets- buy one for 200-300 on one side - transfer it to the other faction it instantly quadruples in value.

Since I've been working on the Insane title I've got a ton of deals on decks in the AH. Bought over 10 this week for less than half their regular price. It's also I guess sort of known that decks go down in value when the faire is gone and up when it is in town.