Oh goodness, how about EVERYTHING? Tho the Sussex Floor Lamp is definitely top of my list at the moment...
For serious and for true, there is a dearth of affordable 1:6 scale mid-century modern miniatures that makes me cry hot, wet tears... But more than that, I tend to create very "everyday" dioramas, and finding things like laundry baskets, cassette tapes, light switches and electrical plates, radiators (my God I'd KILL for a 1:6 radiator!!!) and the like tends to involve days if not WEEKS of scouring Shapeways, evilbay, etsy, Aliexpress, etc. and usually either having to commission something, or try and make it myself if I can.
If you would like to see my current diorama project, you can find it here:
and here are all my dios to date: