They're all pretty exotic and expensive though.
Good wildlife and bird lenses always are (for my value of good anyway, YMMV.) That's why I recommended Canon if they intend on eventually purchasing new long primes, they're significantly cheaper than the Nikkor equivalents (trust me, I paid for a lightly used 400/2.8- I know that of which I speak.)
Although it may displease you, 'D series', 'S series' and 'G series' are terms in common use in the Nikon community.
It neither pleases nor displeases me but having been a member of the Nikon community since ~1992, I can say that it's not "common" in my experience[1]. More
importantly, it's not
helpful to potential or new owners trying to ascertain the availability of compatible lenses *and* it's also potentially confusing since Canon lenses ARE referred to thusly.
In fact, if you use the quoted string "s series" in Google, what you'll find is that every Nikon reference in the first few pages contains "AI-S" or "AF-S," but they are completely outnumbered by the Canon references to "S series" lenses.
This is important because people can potentially use the information here to search for more information and the wrong search string makes it difficult for people to find the information they need or validate the information that's been given.
Furthermore, there are Perspective Control manual focus lenses in the current Nikkor catalog that are listed as D-type lenses-- even the 2008-released PC-E Micro Nikkors[2]. So, at least a few D-type lenses will function exactly the same on the D40 as on a D3x
[1] Nikon uses "D-type" and "G-type" not "series" in its glossaries, but doesn't use "S type-" likely because they used that term previously for a rangefinder lens line and for large format lenses in Copal shutters.
[2] My conjecture is that the distance information is useful for automatic flash as well as the chips being necessary for 3-D color matrix metering, in Nikon-land you need a body capable of autofocus to take advantage of a "D-type" lens, but a "D-type" lens does not need to be AF-D. As far as I can tell the tilt/shift lenses are the only MF-D (made up term) lenses in the Nikkor line, all the other MF lenses are old designs and aren't chipped AFAICT.