Recently, there was just an upgrade including the Copper dragon which is a combination of Lightning and Metal. I personally breed this dragon just using my lightning and metal dragon. Since Metal is on the Right, select Metal dragon first and Lightning second for better results when breeding.
The gold dragon is a legendary dragon, and will be more difficult to breed. It's base elements are metal and fire.
Some reported successful combinations are:
The gold dragon take 48 hours to breed, and another 48 hours to incubate. It becomes available after player level 17. The egg is covered in a gold scale pattern. It can also be purchased in the market for 2,250 gems. It gives 600,000 XP upon hatching.
The most effective method of breeding a steel dragon is using a lichen dragon and metal dragon. This has a 26% success rate. The egg is dark purple with white snowflakes, and takes 14 hours to hatch.
The gold dragon is a permanent legendary dragon, so you can take your time trying to breed it.
You don't breed a Kairos Dragon in DragonVale. You have to get parts to complete it.
You have to either buy it for 500,000 gold, or breed water dragon with another water dragon.
Fire plus metal in the epic breeding cave
you breed a ice dragon with a mine dragon
You have to breed a plant and a fire dragon.
As of July 2012, there has not been a star dragon in DragonVale.
You have to breed a sun and moon dragon together
You have to breed a metal and a water dragon together.
You have to breed a plasma dragon with a salamander dragon.
Breed the earth dragon with the fire dragon.
To get a Smoke Dragon, breed a fire and air dragon together.