Gauntlets of Giantfelling are only like 2000 gp in MIC. 3 charges per day, swift action. You get a damage bonus for 1 round against larger foes, I think it scales up by size difference.
Fell the Greatest Foe, spell in SpC (level 3 for clerics, might be lower for some partial casters). Lasts round/level, target does +1d6 melee damage per size smaller he is than his target.
Counter Charge maneuver in ToB; pick a dex opposed check and get +4 if smaller than the foe.
EDIT: There's also a mid level stance in Setting Sun that gives bonuses to hit and damage against larger foes. I never use it though, because Assassin's Stance + Shadow Blade is just so much better for any small swordsage I'd ever make.