Focussing on the BENE without LUX and Germany (as I have not been to most other regions), there are the following route (per country)::
Belgium: As said: A good chunk of the ICs (e.g. everything between Welkenrath-Liege/Luik/Lüttich-Leuven/Louvian/Löwen-Brussel(s)/Bruxelles/Brüssel (continuing to Gent and Brugge), between Genk-Hasselt-Leuven-Brussel and on the Charleroi-Antwerpen(-Essen), but some are Desiro worked). There are loads of "P"-trains (Peak extras) from Schaarbeek/Schaerbek or Brussel-Zuid/Bruxelles-Midi/Brüssel-Süd/Brussels-South to all sort of destinations, using everything they can find (quite a lot of M4 coaching stock with older and newer locos but some M5/M6 can also be found). The Benelux trains Brussel-Zuid - Amsterdam C are Traxx-Hauled.
Netherlands: Mostly units. There are some Sprinter (stopping) services using 1700s with 70s double-deckers (with a very "nice" green interior). Traxx-Hauled ICs to Brussel and IC-Direct between Amsterdam/Den Haag-Rotterdam-Breda and Eindhoven (via HSL). Then there are the classic ICs Amsterdam-Bad Bentheim-Osnabrück-Hannover-Berlin, which are 1700s to Bad Bentheim and DB 101s from there. The only way to cross from Belgium to Germany by loco-hauled trains is via Amsterdam.
Germany: Every IC (the double-deckers are also loco-hauled sets). A very respectable lot of regional services. In NRW alone there are loco-hauled services on the following lines: RE1 Aachen-Köln-Dortmund-Hamm, RE2 Düsseldorf-Münster, RE4 Aachen-Mönchengladbach-Wuppertal-Dortmund, RE5 Koblenz-Köln-Duisburg-Wesel, RE6 Köln (Flughafen)-Neuss-Düsseldorf-Bielefeld-Minden, some RE9s Aachen-Köln-Siegen, RB27 (Mönchengladbach)-Grevenbroich-Köln-Bonn-Beul-Koblenz - and thats only what springs to my mind at the moment.
To cover some special stuff: there are some loco-hauled IC(E)s using the ex "Metropolitan" stock (
https://en.wikipedia.org/wiki/Metropolitan_(train, numbers are Mo-Su IC1193/1196 (Berlin-Frankfurt(M)), Fr&Su ICE1040/1043 (Berlin-Düsseldorf). S-Bahn Dresden is indeed fully loco-hauled, as are some peak services around Dortmund on S1&S4 and some S68s around Düsseldorf. Some trains still run with "n-Wagen"(REs or RBs) or Bimz(ICs), which are rather classic inside and have decently sized openable windows.
In Austria there indeed all the RailJets and all ICs/ECs and a very fair bit of REX loco-hauled, but I can't comment on that in so much detail.
There are some (cheap) rovers in the threee conutries I know well, which could work out cheaper, if you do not travel through different countries, but there are none for DB long distance services. During Belgish school holidays, it's just 12€ (+ a one time charge of 5€ for the photocard) for a week of network wide travel (under 26). In the Netherlands, some supermarkets sell cheap Rovers (~15€ for unlimited off-peak travel). In Germany (almost) every "Verkehrsverbund" sells rovers and (almost?) every Bundesland has a rover for regional trains as well as nation wide ones. InterRail will however give you the best results when travelling over borders and quite a lot.
Locotypes: There is a huge variety, from classic 70s DB 111s, which are still in service around Stuttgart, on NRW RE4s and on the last remaining service with "Karlsruher Kopf" control cars between Köln and Kaldenkirchen (~6.30 ex Kaldenkirchen, ~16.30 ex Köln-Deutz) to modern Traxx locos in the Netherlands and on other REs. Almost all ICs in Germany are worked by 1990s 101s, which are pretty boring. The same applies to Belgium, with a good mixture of rather "retro" and quite fancy modern locos.
If you have any questions about Belgium, the Netherlands or Germany, I will try my best to answer them.