These are just the ones I was in. Some have been mentioned but I wanted to make some official nominations in the style Tru laid out.
Board # -- year -- X country stabs Y country -- description of the stab (we don't need a novel here :)
Board 3 [
gameID=148789], 1901, Russia stabs England.
-- After a hard sell to England of friendship and eternal loyalty Russia surprises the entire board with the news that he was lying the entire time.
Board 4 [
gameID=151803], 1908, France/Russia stabs Italy and Turkey.
-- After falsely pulling back France gets Turkey and Italy to try to cut out Russia, and then France moves back, side-steps the planned bounce by Tunis, and Russia convoys him to the effective winning centers. Dunno if people more appreciate France's Med side-step and fake-out of dropping the solo attempt, or Russia's spiteful and effective throw. There's some interesting convoys and three-way swaps involved.
Board 7 [
gameID=156118], 1903, Russia stabs everyone, the spirit of Diplomacy, and decency.
--Realizing that there is an overwhelming chance that Russia will get >= 3

for the tournament lead, he bullies everyone on board and in press into a 7 way 1903 draw:
-Germany, who was in a great position, Russia convinces Germany that he'll "play the bad guy" and not draw so Germany can put up his draw for diplomatic leverage.
-England, who was about to kamikaze into France, Russia convinces him that France isn't worth losing his life over
-France actually refused for a bit he was so infuriated with England and insisted to only draw once England was gone but Russia convinced him that Germany would leave England alive as long as he was suicide into France so it would never happen.
-Italy was under pressure and losing centers from the A/R; naturally wanted draw
-Turkey was also under pressure from the A/R; naturally wanted draw
-Austria only friend was a Russia with two centers pressed on his back; naturally wanted draw(?)[He hasn't talked to me since the game even though I PM'd him... =(]