Buxton used to be twin stations side by side, with the Midland half now closed and the LNWR half in use (or at least some of it).
Reading's main concourse (ticket office etc) is built on the site of Reading Southern, originally an SER station.
Oxford Rewley Road (LNWR) was close by the GWR station and survived as a garage for decades, not sure what's left today (the canal swing bridge in the approach still exists I think).
Banbury (LNWR) had Merton St adjacent to the GWR station but I think it's all gone now (track bed towards Buckingham still visible further out).
Leamington Spa Avenue (LNWR) was adjacent to the GWR station and had remains, bridge girders annd viaduct visible for years alongside the GW route.
Bristol Temple Meads was effectively two stations, with the original terminus repurposed by BR with all trains using the through platforms.
The original Bristol & Exeter terminus at right angles to the original GWR/Midland terminus also closed and was clearly visible for many years - don't know what's left today.