In DragonVale for the Android & iOS devices (iPhone, iPad, etc.) the Summer Dragon is a limited dragon available around during.. you guessed it, summer time.
The Summer Dragon has a base breeding time of 24 hours, sells for 1,500,000 coins, and earns 50,000 XP for successful breeding once you reach level 14.
To breed a Summer Dragon, you need to breed dragons that have a mix of water, lightning, and fire elements. Firefly + Water is a good example.