Just starting a thread that can be a repository of links for miscellaneous parts that can be used with and incorporated into any model.
I'll start off by making a generic seat with a texturemap template available for download. (I'm hoping I got the scaling ok. I started out with 1 unit = 1 inch, then converted to 1 unit = 1 meter.) It's in wavefront .obj format, so it shouldn't be too difficult to import and merge with another existing model.
http://www.digitallights.net/models/paul/genericSeat.zip
Added 2/8/2007:
Toggle switch. Retaining nut should be approx 1/2". Scale accordingly.
http://www.digitallights.net/models/paul/ToggleSwitch.zip