I subscribe to many rail-related channels on YouTube. Many of the channels I like have already been mentioned. Like Rich did I broke down my picks to Prototype and O Gauge and limited to my top three of each.
Prototype: Love all three because of the great camera work and coverage of east coast & mainline steam.
Eastern PA Railfan Productions
O Gauge:
pennsy484 - Great collection of PRR Steam
pghTrainFanatic - Loved watching Nick's process of building a top-tier layout throughout the updates
I also really enjoy Virtual Railfan's Strasburg Camera. Non-train related but if you are a home-improvement/DIY guy, This Old House has a channel with how-to videos as well as full episodes of their show; I love watching their videos.
And of course, before the end of my post, here is a shameless plug for my own channel; I post a variety of prototype, O gauge, and G scale. I'm working on getting better at filming, and hope to one day have videos as good as the channels I listed above.
