If you go the Strat-O-Matic route I am currently in 3 online leagues using the PC version of the game, I suggest you play the board game and once you understand the ratings and how results are derived upgrade to the PC Game.
Anyway here are a few leagues websites I participate in we have openings every so often:
http://www.cshl.byethost5.com/CSHL.html?i=1
http://www.nsohl.com/
http://usfleagues.net/