I'm short on time this AM so no full top 10 list, but here's an abbreviated list of "chokes" that stand out in my head.
1. '99 British, Van de Velde (the name is now a synonym for "collapse").
2. Greg Norman, 1996 Masters
3 Phil Mickelson, 2006 US Open
t4. Kenny Perry, 1996 PGA & 2009 Masters
6. Tom Lehman, 1996 U.S. Open
7. Tom Watson, yesterday
(1996 was a year of gags...never realized it)