- Vintage jewelers are a good options because it's re-using what's already been mined. Check out Antique Jewelry Mall
- UK jeweler Harriet Kelsall is a member of the Council of Responsible Jewelry Practices
And in case you want to read more discussion, the wedding blog Manolo for the Brides has a post called "What's Love Worth?" - does how much one spend on a ring represent one's love? There's also an interesting discussion on diamond engagement rings at the Vegan Represent Forum.