Hands down, I have to say that the most interesting train I have ever seen was on my birthday in 2002.
With my avid train-watcher boyfriend, we caught a 10-diesel NS coal train at Speer's Ferry in Virginia consisting of:
LLPX 2804-SD38-2
HCLX 7933-"Furby" SD40-2, I believe
BNSF 4340
NS 8437-Conrail paint
Santa Fe 689-Warbonnet scheme
BNSF 4631
BNSF 763-Warbonnet scheme
Santa Fe 647-Warbonnet scheme
Union Pacific 4489-winged SD70
Union Pacific 9183-C40-8, I believe
(You'll notice that there is actually NO true NS listed). This was my first sighting of most of these schemes...also a first, down the line at Bootleg Trestle, we met Chris Starnes and Ron Flanary chasing it.
To see any shots, look up photo ID 25 on RP.net...or email Chris Starnes, whereas he's deleted the shots from Bootleg to conserve space.