In no particular order:
NFL Conference Semifinals (this weekend): even though the NFL has taken a backseat in recent years in my world, the 8 best teams in the league evenly spaced over the weekend is tough to beat.
Whenever New Year's Day falls, with all of the great college bowl games (since NYD is a holiday, I am counting it as a weekend).
Weekend #2 of March Madness: Still get plenty of games, usually great teams, and the occasional intriguing Cinderella. I like this weekend over the Final Four for the same reason that I like NFL Conference Semis over the Conference Finals: more games.
IAAF World Championships: even better when we can get it on TV.
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Obviously, the Summer Olympics and the World Cup are pretty fantastic, but they take up well over a weekend; and the Super Bowl, etc. aren't enough to fill up an entire weekend.
How about for you? What weekends (or other short time periods) do you really look forward to each year or two?