In my depictions of characters and situations in Planescape, the typical technology used is somewhere around the 19th century. Though it's the fantasy version, steam-tech and all that with some so-called magi-tech as well. A lot of the stuff that existed around the early half or the 19th century is conventionally developed, some in common use, some not. The technology is sort of all over the place with it being quite developed in some areas, and less developed in others. Electricity is used for a select number of things and is a new development, while mechanical devices just get more and more complex.
Some things that were invented in the 19th century are listed here.
With the help of magic, psionics and other supernatural forces, things beyond the capability of 19th century technology exist such as airships and flying machines of various kinds. They become a very in demand form of transportation, as militairies and other groups start getting armadas of airships. The Analytical Machine, essentially a mechanical calculator is turned into a Thinking Machine with the power of the supernatural. Artificers rise in significance. And parties of adventurers come equipped with all sorts of weapons (percussion cap firearms), and strange devices, finding stranger and more mysterious devices on other worlds (some even beyond the 19th century, though really advanced devices often don't work or are altered by reality itself to be less advanced when taken from their worlds).
Think of the CRPG Arcanum in terms for the way how some things are...
So anyone have more ideas to go with such developments? Or more such items to be used?
Some of the things from d20 Modern, particularly the demon-posessed machines, seem apt. Especially since Planescape already has a demon-posessed machine: Grundlethum's Automatic Scribe.
If you've read Perdido Street Station by China Mieville you'll see a lot of other interesting uses of steampunk and sorcery.