One book I use as a rough guide is Leonard Maltin's VideoGuide that usually mentions if a special (non-spherical 35mm) process was used, and of course, the year. Combining the two you can usually determine the aproximate aspect ratio the film was projected in, including most Disney movies.
Here's my own list of Aspect Ratios.. The year cut-off dates are aproximate:
1- Silent films 1.333
2- Early sound films (up to about 1931): between 1.17 and 1.375
3- Academy sound (up to around 1955) : 1.375
After around 1955 unless a "special" format is mentioned, it was probably shot with "Academy like" cameras, but in "open matte" or "hard matte" widescreen variations, their aspect ratios usually being, (but not always):
4- USA widescreens: Shot "hard matte" 1.85 or "open matte" 1.375, but composed and intended to be projected at1.85.
5- European widescreens. Shot "hard matte" 1.66 or "open matte" 1.375, but composed and intended to be projected at1.66.
6- Disney widescreens. Shot "open matte" 1.375, but composed and intended to be projected at around 1.75, the average of the previous 2 aspect ratios for maximum compability in both markets; or rendered in the CAPS system at 1.66, usually projected at 1.85.
TV programming kept being shot in Academy ratio (with allowances for TV's "safe action area") till recently, now slowly changing towards the "HDTV" aspect ratio of "16:9"
Then we have the special widescreen processes which are many but fall mainly into::
7- CINERAMA (only 2 movies): 2.59
8- VistaVision: shot in 1.5, composed and intended to be projected at 1.85
6- Technirama: Shot at 2.25. Projected in 2.35 Scope, or 2.20 70mm.
9- 70mm Todd-AO/SuperPanavision: 2.20
10- 70mm Camera-65/UltraPanavision: 2.75
Plus the zillion "scope" processes that use various negative formats but are projected as "Scope" (Anamorphic 2x lens) prints:
non scope negative:
11- Superscope: Shot in the silent 1.33 aperture but composed and intended to be projected at 2.00
12- Superscope 235: Shot in the silent 1.33 aperture but composed and intended to be projected at 2.35
13- Super-35: The current "son of Superscope" process we have today, which is usually used for Scope prints (but not always, sometimes used for standart widescreen 1.85 movies too) shot with the silent aperure 1.33 but composed and intended to be projected at 2.40 or 2.39 (depending on year, see below)
14- Techniscope: 2.35 or 2.40 (depending on year, see below)
true scope negative:
15- Magnetic Cinemascope (up to around 1956): 2.55
16- Optical Cinemascope/Panavision (1956-1970): 2.35
17- Optical Panavision (1971 -1994): 2.40
18- Digital Panavision (1995 -today): 2.39
19- Also the rare 55mm shot Cinemascope55 (2 movies): 2.55
(Several format names are equivalent: Cinemascope, Panavision, Arrivision, etc etc.. When it says at the end of the movie "Filmed WITH Panavision cameras and lenses" it usually means standart "academic"1.66-1.85 widescreen as opposed to "Filmed IN Panavision" which means filmed in 2.xx "Scope")
Oh, and there's one more "aspect ratio", #20: Abel Gance's silent movie Napoleon which in it's last reel widened to three x 1.33 = 4.00
Formats 4, 5, 6, 8, 11, 12, and 13 could all possibly have "Fullscreen" open matte video versions that show more of the vertical image than intended, if the camera negative wasn't shot with a hard matte.
As disneyunlimited wrote:Watching it on a widescreen TV will chop off the top and bottom but that isn't a problem as being "framed" by the director for 1.75:1 means you WON'T be chopping off peoples heads AND you're seeing it in as near as dammit the same ratio as the cinema version
So you should try that on some of your "Fullscreen" post 1955 movies and see if it works
Also, keep in mind most TV's have some form of overscan, so they are already cropping/chopping off some percent of this vertical "open matte" area that's not supposed to be seen, but since they also chop/crop part of the width that IS, an open matte transfer might look like it's a little pan/scanned, while all it needs is to eliminate the extra vertical space to become widescreen
hope this helps
') cardboards on front of a 4:3 display, or use the zoom feature in a 16:9 display, and he would get the exact same thing as a 4:3 "letterboxed" widescreen transfer, while the ones that don't like the "evil" black bars wouldn't get them. 
) 
