Anand's 59. ...Rg3?? turns win into loss (was it blindfold?)
Piket vs Anand, 1998
(D86) Grunfeld, Exchange, 60 moves, 1-0
Short's 120. Re6?? flushes his long, hard fought game
Short vs Krasenkow, 2004
(B33) Sicilian, 122 moves, 0-1
Aronian ends game with rank beginner back-rank blunder
Aronian vs Svidler, 2006
(D80) Grunfeld, 24 moves, 0-1
With 87...Ke6, GM Conquest walks into mate
A Cherniaev vs S Conquest, 2004
(B22) Sicilian, Alapin, 88 moves, 1-0
With 34...Qe3??, the new Chess World Champion allows mate-in-1!
Deep Fritz vs Kramnik, 2006
(D20) Queen's Gambit Accepted, 35 moves, 1-0
Top GM botches a simple K+2P vs. K ending with 76. c6? - draw!
Dreev vs R Wessman, 1990
(D45) Queen's Gambit Declined Semi-Slav, 77 moves, 1/2-1/2
I guess it can be considered a blunder to resign a drawn game..
R G Hegde vs Palatnik, 1988
(E17) Queen's Indian, 59 moves, 1-0