The Colchian dragon isn't the only dragon protecting treasure in Greek mythology. A couple more examples: 

- [Ladon][1] guarded the golden apples in the garden of the Hesperides,
- [Python][2] guarded the [centre of the earth][3] at Delphi, and
- Ares assigned a [dragon][4] to protect his sacred spring near Thebes (look up the myths of [Cadmus][5]). 

However, if you are looking for a dragon protecting gold specifically, then I think the more characteristic examples from European folklore are:

- [Fafnir][6], the dwarf-turned-dragon in the [Völsunga][7], and
- The [firedrake][8] in [Beowulf][9].

In fact, unless I'm horribly mistaken, the latter one is the inspiration behind [Smaug][10], the gold-hoarding dragon in J. R. R. Tolkien's *The Hobbit*.


  [1]: https://en.wikipedia.org/wiki/Ladon_(mythology)
  [2]: https://en.wikipedia.org/wiki/Python_(mythology)
  [3]: https://en.wikipedia.org/wiki/Axis_mundi
  [4]: http://www.theoi.com/Ther/DrakonIsmenios.html
  [5]: https://en.wikipedia.org/wiki/Cadmus
  [6]: https://en.wikipedia.org/wiki/Fafnir
  [7]: https://en.wikipedia.org/wiki/V%C3%B6lsunga_saga
  [8]: https://en.wikipedia.org/wiki/The_dragon_(Beowulf)
  [9]: https://en.wikipedia.org/wiki/Beowulf
  [10]: https://en.wikipedia.org/wiki/Smaug%5C