You can easily sell Jewelcrafting designs to oblivious people by buying a vendor recipe and then just putting it on the market for double its value or more.
Here's the list of Jewelcrafting designs:
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Design: Amulet of the Moon
Sold by: Mythrin'dir - Darnassus
Daniel Bartlett - Undercity
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Design: Pendant of the Agate Shield
Sold by: Jandia - Thousand Needles/Hillsbrad Foothills
Neal Allen - Wetlands
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Design: Wicked Moonstone Ring
Sold by: Dalria - Ashenvale
Ranik/Jazzik - The Barrens
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Design: Heavy Iron Knuckles
Sold by: Christopher Jeffcoat (Horde), Micha Vance (Alliance) - Hillsbrad Foothills
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Design: Blazing Citrine Ring
Sold by: Kireena - Desolace
Micha Vance - Hillsbrad Foothills
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Design: The Jade Eye
Sold by: Burbik Gearspanner - Ironforge
Felicia Doan - Undercity
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Design: Truesilver Crab
Sold by: Nerrist - Stranglethorn Vale
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Design: Opal Necklace of Impact
Sold by: Burbik Gearspanner - Ironforge
Shadi Mistrunner - Thunder Bluff
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Design: Emerald Crown of Destruction
Sold by: Mishta - Silithus
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Design: Necklace of the Diamond Tower
Sold by: Qia - Winterspring
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That's all available at the moment from vendors, in order by their price. I'm nearly positive every single one of them is also only a Limited Quantity (1).