Not sure... it may help if you gave a hint about what you my be looking for.
THIS PAGE makes a pretty good start, IMO. But I would still hold onto the idea that best ones are custom work commissioned from independent jewelers. And from that perspective, browsing pret a porter designs is about half the task.
You may find a few sources of custom work with a good amount of feedback on the ''Show me the ring'' forum.
Art of Platinum, Mark Morell (mwmjewelry.com) come up often, Whiteflash turned quite a few applauded custom orders recently, Quest... and a few others.
Among the reliable Pricescope e-ring recipes, having a diamond set in a temporary setting and letting the lady decide is one way to go. Makes life easy, apparently - as much of the techie quality checks end with the diamond, while settings involve more personal choice. And sometimes innovative choices turn painfully wrong (like it happened here).
Not that you have much of a chance to go wrong with a very classical, nicely executed option (E.G.), but if you know a more unusual style may be particularly appealing, maybe it makes sense to ask for hints, or let the end user choose their own.
Of course I don''t know anything about the particular situation. Just a thought.