Here's a quick grab-n-go list of some gems with a little bit of description, sorted by some handy value tiers. As a reminder: gems are so trivially small that unless you're dealing with handfuls of them, you can ignore the weight. I've included weights anyways in case you want like, a pound of obsidian trade gems or something.
( Read the great big list... )By the by: that pound of obsidian rupees is 333 rupees, or $8 325. And now you know!