Stability weights (Underdark 66) (160 gp; 30 lbs.), in addition to other effects, lower an armor's maximum Dexterity bonus by an additional −1, making it so, for example, if installed on half-plate (Player's Handbook 123, 125) (600 gp; 50 lbs.), that armor may have a maximum Dexterity bonus of −1.
I say may because I don't know if that's really possible. No published armor—even the most grotesquely heavy armor, thaalud stone armor (Anauroch: Empire of Shade 108) (2,800 gp; 180 lbs.)—has a maximum Dexterity bonus of less than +0, but the Armor and Weapon Template hellforged says, "The maximum Dexterity bonus granted by hellforged armor or a hellforged shield is reduced by 1 (minimum +0)" (Dungeon Master's Guide II 278), and that parenthetical minimum 0 leaves me wondering.
Can armor's maximum Dexterity bonus be less than 0?