Two shelves in the situation room (back)
A shelf aboard the Fortunate
A shelf was an open storage piece of furniture.
Kitchens were often equipped with shelves and books were often placed in shelves. (ENT: "Observer Effect", "These Are the Voyages..."; VOY: "11:59"; TNG: "Brothers")
A shelf in the reliquary at the monastery
The reliquary in the catacombs beneath the Vulcan monastery at P'Jem was filled with shelves which had artifacts, relics, statues, and other Vulcan objects in it. (ENT: "The Andorian Incident")
Aboard the NX-class starship Enterprise NX-01, shelves could be found in the galley, crew quarters, sickbay, and in the situation room on the bridge. (ENT: "Broken Bow", "Terra Nova", "Civilization" et al.) In the quarters small shelves were placed over the beds. Most crewmembers placed books and personal items into these shelves. (ENT: "Breaking the Ice")
A shelf pod from one of the quarters was later sold off on the It's A Wrap! sale and auction on eBay. [1]
The infirmary aboard the Earth Cargo Service freighter ECS Fortunate was equipped with shelves which were used to store medical supplies, jars, and thermos. (ENT: "Fortunate Son")
In 1999, Shannon O'Donnel asked Henry Janeway what he had won by fighting the building of the Millennium Gate: "The right to hide behind these shelves for the rest of your life?" (VOY: "11:59")
In 2154, Trip Tucker recalled his folks putting all the kitchen appliances on the highest shelves when he was a child so that he couldn't reach them and disassemble them. (ENT: "Observer Effect")
In 2284, James T. Kirk kept oregano in the same cabinet as dill weed. When trapped in the Nexus with Jean-Luc Picard, he asked Picard to bring him the dill, which he said could be found on the second shelf to the left behind the oregano. (Star Trek Generations)