Populate this with suggestions. 

I think Fangraphs, Baseball-Reference, and Baseball Prospectus are known and don't need links.  Baseball Savant, Brooks, other useful sites probably can be linked in general.

Nats specific sites with stats, rankings, and game stories would be useful in this post, but frankly I'm bad at that so will want postings below and links will be pasted in here by either me or Imref.

For example: https://nationalsprospects.com/ - nice overview of the system and home of the Big Board that keeps up on all the players around the system.

Finally, news sites in the minor league towns like Fredericksburg are also good sources.