These are some I remember:
John McEnroe has a conflict with the umpire, leaves the court and never comes back (during the match!); oponent was Mecir, I think.
Tim Mayotte goes mad when he loses a point because of an over-rule against Edberg at 11-11 in 2nd set tie-break. Controversy lasts several minutes, then he loses set and match.
1990 Australian Open
In 4th round against Perfors, John McEnroe forgets new rule which only allows 2 warnings instead of 3. When he says 'f***' to the umpire he expects to get a game-penalty, instead he is disqualified.
Brad Gilbert and David Wheaton almost starting a fist-fight during 3rd set tie-break of their semifinal. Not surprising, because the finalist is guaranteed 1 million $.
Of course there are many others, like Jeff Tarango once calling Bruno Rebeuh (sp?) 'the most corrupt umpire' and his wife slapping Rebeuh later.
What's your favourite incident ?