Make Gold with Engineering

Engineering is a fun profession that is used to create all kinds of toys and gizmos. A lot of the items that can be made with engineering are bind on pickup, which isn't good if you want to make gold. If you want to make serious amounts of gold I wouldn't recommend engineering, but it's not all about gold for everyone. Many players like using gadgets like Nitro Boosts, Parachute Cloak and Hand-Mounted Pyro Rocket. However there are a few things that you can sell to make some supplemental income.

As of patch 3.3.3 Pet Bombling and Lil' Smoky are no longer bind on pickup and can be sold to other players. The price has already dropped a bit on my realm but you can still get 100 gold or more for them.
  
The Mekgineer's Chopper/Mechano-hog cost about 13 000g to make, but can usually be sold for around 16 000 or more gold. Selling these mounts used to be able to make an engineer a fortune shortly after the launch of WOTLK, but now there isn't a lot of demand for them so it can be difficult to find a buyer.

There is a quest in Borean Tundra and The Storm Peaks which require Overcharged Capacitors. These go for about 20 gold and they sell fairly quickly.