tennis, no contest...
Tennis is the greatest sport to play oneself (Golf is for old-timers that can't play tennis anymore), and one of the best to watch as a sporting event as well.
http://www.atptennis.com/5/en/tournaments/fullcalendar/
May is the month for clay!
With any luck, there'll be some Federer v Nadal to enjoy.
May ATP events:
5/7/2007
ATP Masters Series Rome Italy
5/14/2007
ATP Masters Series Hamburg Germany
5/21/2007
Poertschach Austria
5/21/2007
World Team Championship Dusseldorf, Germany
5/28/2007
THE FRENCH OPEN Grand Slam
Roland Garros Stadium
Paris, France