Almost every dragon that appears across the three series is related to a set of Dragonballs. Shenron is the dragon seen the most, as he comes forth to grant a wish every time that Earth's set of Dragonballs are brought together. Shenron's look is that of a traditional Chinese dragon.
The Namekian Dragonballs summon the dragon called Porunga, who is huge bulky dragon that looks a lot more humanoid that Shenron, apart from not having any legs. The dragon related to the Black-Star Dragonballs was an alternate version of the original Shenron, who instead is coloured red, and is multiple times larger.
In Dragonball GT when the Earth Dragonballs became filled with negative energy, a black dragon appeared who then split into seven other dragons, one for each of the Dragonballs. Goku and Pan set out to defeat each of these dragons, and the majority of them were very weak.
Related ThreadsTaming the Dragon - last post by @ Mar 5, 2012
Dragon Quest (spoilers) - last post by @ Nov 18, 2012