I too am addicted to glass. I absolutely love the dark-cyan color of clear glass, and tend to use it to make elaborate constructions. I can't recall my last fortress that didn't chiefly export glass goblets for the first few years.
Also: Underground water features and some sort of water source. I'm at a loss as to what to do with my legendary miner after digging out my functional fortress if not turn every level below the water source into layer upon layer of gigantic towercap nurseries.
Along those lines- a way to drain the water- that is, a chasm or pit of some sort. I've rigged up an elaborate pumping system to drain water off the edge of the map (on the surface) once before, and I never want to do it again.
That's it for features (the magma requirement is a given).
I have, however, become addicted to really, really small fortresses after playing in a 2x2 featureless haunted forest (for the silver barb dye and phantom spider silk), and playing at 100 fps, even when I had ~50 dwarves! After several control tests (starting otherwise identical maps with rivers, magma vents, cliffs and the like), I found that high cliffs and larger play areas are hundreds of times more important to the fps than temperature, weather, or units. (Flows are just about as influential if there's something up, but as long as they're stable they're generally fine.)
Basically, my fortresses now have to be 2x2 with no more than 3 or 4 Z levels on the surface. They also have to have sand, plenty of trees, magma, and an underground water feature/chasm (preferably the end of a cave river).
Once you've found that fortress tell me, as I'd love to start playing again. It's actually pretty easy to find such a site without the water feature/chasm, but since those types of things only show up under mountain tiles... Well... I've been looking for a while.