Inner Message Ring
Ring with letters on the inside that leave a message on the finger. [link]
This fake moustache ring will be useful in all kinds of situations. [link]
Plug and Socket Rings
Awesome ring designed by Chutapat Wittaya from Thailand. [link]
Ring with ocean waves in contrasting white and yellow gold. [link]
Ring with gears that turn in unison when the outer rims are spun. [link]
For even more inspiration, check out: brilliant ring designs.