Many of the characters in The Hobbit find their ethics challenged by greed.
Smaug is almost defined by greed. His hoard, in a sense, controls his life.
Dwarves: The dwarves as a race balance between ethics and loyalty and greed, with the greedy aspects of their characters serving to foment dissension in the group. Thorin, in particular, in coveting the Arkenstone makes many mistakes.
The One Ring: inspires greed in its possessors which almost destroys Gollum, and is seen to begin to affect Bilbo. This theme is developed more in Lord of the Rings.
Bombur's greed for food drives a few minor comic sub-plots.