Can think of a few notable examples on the Strathclyde network. Not that they come anywhere near close to some of the examples already cited here, but hey-ho.
- Shieldmuir on the Argyle Line. Not so much when looking towards Motherwell (trains are still somewhat visible as they round the bend through Motherwell and under the Merry St bridge) thanks to two gentle curves between the two, but trains coming in from the south on the Wishaw Avoider* can be seen rounding the curve near Overtown from Law Junction - roughly 3 and a half miles away - in the right conditions.
- Garscadden on the North Clyde & Argyle Lines. Looking east, trains can be seen as they approach Scotstounhill - another contender for this thread - from Jordanhill and looking west, from Yoker. Granted, there's barely a mile and a half between the 3 stations, but an example I thought was worth a mention all the same.
- Cardonald & the two Hillingtons (East & West) on the Inverclyde & Ayrshire Coast Lines. Cardonald in particular is noteworthy among these 3 stations, as on a clear day, trains can be made out before they pass under the
M77 slip road (for the junction with the M8) looking east and before they call at/pass through Hillington West looking, well, west (the line curves off towards Arkleston Junction just beyond the latter).
Attached images are from a visit yours truly made to Cardonald on a hazy/overcast day in May 2017. Not the greatest illustration thanks to said weather, but they give one some idea as to how far out trains can be spotted. Not that it matters with the above in mind - plus all 3 stations are kitted out with passenger info systems; tannoy & displays on both platforms - but you generally can't clearly hear the trains coming at Cardonald until they're close to or within the platfom limits, thanks to it being bounded on 2 sides by the M8 and Berryknowes Road respectively.
*: Not a official name for that section of the WCML I know, but one I coined (along with a simliar name for the section between Uddingston Junction & Motherwell avoiding Bellshill & Mossend Junction) to make my own life easier lol