If I were to exclude holiday deals, and concentrate on a single deal for a specific game, I'd have to nominate Toys R Us for the deal they had for Mortal Kombat. Only a week after release, they had it for $39.99, and you could save an additional $10 with the in-store coupon. Hell of a deal for such a new game.
Also, the TRU 2 $60 games for $50 snafu.