openrailwaymap.org is amazing. even shows electrification and maximum speeds

OpenRailMap is good all around.

• For Canada, check out the Canadian Railway Atlas. Works pretty fast, eh.
• For USA Class I Freight rail, check out this map. (Note it is very slow to use). USA national passenger rail Amtrak's system map/trip planner is here
• For Mexico, check out the Mexican Government ARTF's Sistema Ferroviario Mexicano interactive map (Also very slow). On the flip side they offer a direct download to their map files as well.

This is the best one I've found in the UK:

https://railmaponline.com/

The site appears to be adding US railroads as well but I don't know how complete it is.

The UK map has lots of layers so for example you can turn on/off disused railroads - we have lots of these, a large number of small lines across the rail network were abandoned in the 'Beeching cuts' in the '60s. There are also layers for the new HS2 high speed railway (including parts that have been cancelled!).