Here are the series that I know of on the net.
What to do: Point your browser, read stuff and SIGN UP!
INDYCAR:
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Internet IndyCar Challenge(IICC):
http://www.racesimcentral.net/
IndyCar Racing Series(ICRS):
http://www.racesimcentral.net/~sabata/icrs/index.html
NASCAR:
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Internet Winner's Circle Championship(IWCC)
http://www.racesimcentral.net/~iwcc/welcome.html
Internet Grand National(IGN):
http://www.racesimcentral.net/~pinniped/
-- Terje Wold Johansen "I am your inferior superior." --
-- Dept. of Informatics --
-- University of Oslo, Norway --