List curated with Chris Low
Chief Delphi: https://www.chiefdelphi.com/ Where FRC people gather to talk
Discord: https://discord.com/invite/frc Where you can get answers very, very fast. This is where I go for one-off questions, and is the most valuable way to get students to learn on their own time (I'm biased, it's how I learned and I am a moderator over there.) https://discord.com/invite/frc
The Blue Alliance (aka "TBA"): https://www.thebluealliance.com/ look up any team - some of their history, links, etc.
Statbotics: https://www.statbotics.io/ newer statistics website of comparing teams
https://www.andymark.com/ (Indiana)
https://wcproducts.com/ (California)
https://www.revrobotics.com/ (Texas)
https://www.mcmaster.com/ (Everywhere)
https://www.onlinemetals.com/ if you can't find a good local sheet metal and box tube supplier
https://www.eplastics.com/ if you can't find a good local polycarbonate supplier
Wire - https://powerwerx.com/ needs to be copper stranded wire, please don't use Amazon (very likely you will get "illegal" wire)
https://www.frcdesign.org/ - start here!
https://onshape4frc.com/ - this also works!
FRC 3847 - First Tool Purchases for FRC Teams on a Limited Budget: