Now with patch 3.3.3 Engineering Pets are not exclusively for Engineers! Great for the avid pet collector and even better for Engineers who want to make gold.
On my server, the following pets commonly sell for 200g +
Lifelike Mechanical Toad
Pet Bombling
Lil’ Smokey
Tranquil Mechanical Yeti
You can also sell Mechanical Squirrel Box for about 10-20g each.