AutoBuy

Automatically buy goods, such as reagents or water, from vendors. Last updated: Works on Cataclysm. (Dec 24, 2010)

For example, mages set it to keep 20 Rune of Teleportation. If you have 15 in your bags when you talk to a reagent vendor, it will automatically buy you an extra 5.

If items are sold in sets of 5, for example, it will not over buy: Wanting to buy up to 20 waters (sold in 5s) with 11 in your bags will only by 5.

Usage:

Type in the following command in WoW to buy 20 of some item. /autobuy <link your item here> 20

View current items to buy: /autobuy list

Clear current list: /autobuy clear