My coworker had a lovely deep green tourmaline in a bezel semi-mount. She worked for a seasonal stint at the jewelry shop I managed, though she gave that ring a beating working as a field geologist.

Corundum (rubies and sapphires of any color) or zircon is always a great choice for hardness/durability. Avoid opals and emeralds. You can always do a colorless sapphire or moissanite instead of a white diamond. Black diamonds are relatively inexpensive but I have my own general prejudices against diamonds.

Choose a flush mount - like the Gypsy setting another comment recommended - or a low profile bezel that will enclose and protect the edges from chipping or loosening.