Magma channels. An elegant way to power forges without having their magma source drain away when you expand is to dig 1x1 channels in your forge room where you want to put the workshops, then pump a small amount of magma into the room itself so that it fills the holes and then evaporates from the floor. You'll be left with independent power sources for your forges and also get rid of the non-magma-safe stones in the room.
Trade depot. If you can design it so it fits into a shallow pit with ramps down to it, you can then cover it with a bridge to protect the traders, or use it to drown them. You can also build a walkway above it with a garbage zone defined, and then dump all your crafts/junk you don't want to use there. When traders come, unforbid what you want to sell and then move it to the depot (it will be distance 0) - it'll clear out your stockpiles quicker, the Dump Item job is higher priority, and you can have one idle dwarf (the broker) do all the Bring Item to Depot jobs at once. Even if you prefer trading a couple of gold figurines for the entire caravan, you can gift away all the junk they are able to carry, rather than atom smash it. It's especially useful if you do a lot of gem setting because the jeweler won't pick up trading goods or forbidden items, and if you've dumped everything except the masterwork pieces then they can't really get it wrong.