Just an idea: a stickied thread, updated regularly, listing all the available (and competently run) NS leagues with links to the websites.

I figured this would already be in the League/Tourney forum, but I searched and found nothing, so pardon me if I'm blind and missed it!

The only one I'm familiar with is CAL;

Main Site: http://www.caleague.com

NS Section: http://www.caleague.com/?div=natsl

http://www.esl-europe.net/ (ladder and currently running opening cup)
http://www.clanbase.com/ (several ladders and now running open cup)

If you'll look up at the stickied topics you'll find four leagues listed along with their links

• UGL
  
• CAL
  
• OGL
  
• ClanFission