What are the best resources for exploring nostr?
What are some of the best websites for getting started with nostr?
Where should I send Norm to onboard?

Code repository for the protocol itself
https://github.com/nostr-protocol

Editable public encyclopedic summary
https://en.wikipedia.org/wiki/Nostr

Overview Summaries / Get Started onboarding / Recommendations for starter clients & apps
https://nosta.me/
https://nostr.com/
https://nostr.how/en/what-is-nostr
https://nostr.info/
https://usenostr.org/
https://nostr-resources.com/

Apps Directories
https://www.nostrapps.com/

Nostr Profile and Relay Directories & Stats
https://nostr.directory/
https://nostr.band/
https://nostr.watch/relays/find

Can't much edit the above myself as you all add your recommendations, but this list ought to be copy and pasteable and useful for sending along.