In the US, are there any operational control towers located in surface-level Class E airspace or in Class G airspace? (This question pertains to the airspace of the United States.)
FAR 91.126 gives some general rules for operating at or near airports in Class G airspace, and FAR 91.127 gives some general rules for operating at or near airports in Class E airspace.
Section (d) of 91.126 and section (c) of 91.127 pertain specifically to operations at airports with operational control towers.
a) This seems to beg the question, are there any operational control towers located in surface-level Class E airspace or in Class G airspace?
b) Were there ever?  (Counting from the September 16, 1993 &quot;alphabet&quot; airspace re-organization onward.)
c) If &quot;no&quot; to a and b, then what is a practical example of how a pilot's behavior might be altered by the need to comply with 91.126(d) or 91.127(c)?  After all, it appears that generally speaking, it is not possible to get within 4 nautical miles of an airport with an operational control tower, at 2500' AGL or below, without entering Class D (or higher) airspace.
There are a handful of towers still in Class E/G airspace. They're rare, but they do exist and are something to watch out for during preflight planning.
As of April 2021, here's the airports I know of:

KJYO - Leesburg, VA
KPCA - Picacho ARNG, AZ
KTNX - Tonopah Test Range, NV (inside restricted airspace)

I wouldn't be surprised if there's others I missed, these aren't really cataloged anywhere.
Many of these do eventually become proper Class D airports once they have proper weather reporting capability. For example, KTRK (Truckee, CA) was an infamous one on the west coast that just got its Class D ring in 2017.
You'll also see temporary towers pop up via NOTAM for special events. These NOTAMs don't change the airspace designation, since changes to airspace need to go through the formal rulemaking process.