http://www.tlotr.com/tolkien_art/index.php
http://anduin.eldar.org/artgallery/tolkien/
Here are a few (rather small) archives of Tolkien-related art, in which you should probably be able to find some dragon drawings. You could also check the Barrow Downs' own links site or even the Reader Art section of Barrow Downs. There are some very lovely drawings of Scatha, Smaug and Ancalagon (three prominent dragons in the world of Tolkien), among others, in the Reader Art section.
To add to what Lady Snickerdoodle said, dragons do generally horde wealth from cities or halls they have overthrown. Dragons began as the servants of Morgoth in the First Age, the captains of his fell armies. Glaurung was their chief back in the day, a treacherous bloke who was as powerful and crafty of mind as he was physically mighty. Originally, dragons did not have wings, but rather probably looked something like fat reptilian worms with claws, mantles, and teeth.
Then came the fire-breathing dragons and the dragons with wings. When Morgoth's halls were emptied in the War of Wrath at the end of the First Age, Ancalagon the Black, the mightiest winged dragon and (probably) the largest and strongest dragon ever, led the host of the winged dragons against the forces of the Valar, but was defeated by the blade of Earendil.
After the First Age and the ousting of Morgoth, their numbers dwindled greatly, and they took to their mountain-hiding, wealth-hording ways. Smaug was the last dragon to appear chronologically in Tolkien's works. He was defeated by Bard the Bowman in
The Hobbit after being driven from the Lonely Mountain by Gandalf the Wizard, Bilbo Baggins and a host of Dwarves.
Of course, this all sounds like complete mumbo jumbo if you are not really familiar with Tolkien's works, but I hope that helps. Welcome to the Downs.
Cheers,
Angmar