Items and Feats for Opposed Trip Checks

[Telonius]

I'm trying to design a trip-based enemy for my players, and am coming up a little short on ideas of how to boost the opposed check. For RP reasons, the enemy is a Drow Duskblade18, Dex-focused, with a Weapon Finessed Spiked Chain. (Dex 24, Str 18). The above can't be altered; but the Strength score is not yet modified by any items or buffs, and the Dex will be up to 28 thanks to an item. He won't have any trouble hitting them, but I'm concerned that he won't actually be able to win the opposed check against some of the stronger PCs. Our front-line melee guy has a strength of 24 at the moment, which can be fairly easily buffed a lot higher by the Cleric. Secondary melee guy is a 22-STR Dwarf.

So far, I've found these methods of improving the opposed check:
Size increases (Potion of Enlarge Person, etc)
Strength increases (Potion of Bull's Strength, Manual of Gainful Exercise, etc)
Improved Trip feat
Armbands of Might (MiC)
Brute Gauntlets (MiC)
Sweeping weapon enhancement (MiC)
Torc of the Titans (MiC)

Google-fu is weak, and I haven't been able to locate a trip optimization guide. Is there any other item or feat that will grant a bonus on the opposed check?

[Person_Man]

All you're really missing is Knock-Down (http://www.dandwiki.com/wiki/SRD:Knock-Down).

You could also look at Sand Snare from Sandstorm, which makes it much harder for the enemy to stand up. But it requires that they be standing in sandy-ish terrain, so you really need to partner with someone using the Earth to Sand spell or Decanter of Endless Sand from the same book.

But as a general commentary, I would say that Dex based builds aren't very good at your standard Trip, Bull Rush, or Grapple. There are two exceptions though. One is Tome of Battle, which includes manuevers that Trip without an opposed check. The other is Confound The Big Folk from Races of the Wild, which allows you to make a Trip check against an enemy that's bigger then you by using your Dex and ignore size bonuses. But it requires a Standard Action, and in general you to be a really small race so that you always qualify. Along the same lines there's a good racial feat in one of the books that requires you to be a Dwarf or Gnome and auto-Trips your enemy if you're attack the from above (works great for Dragonborn). But again, that would require a change you wouldn't allow.

[Gandolfi Feesh]

Take a level in Exotic Weapons Master, one of the tricks allows you to make trip attempts if your exotic weapon doesn't normally allow it, or a +2 to trip attempts if it already has this ability.

[faceroll]

Do you really need 18 levels of duskblade for "RP reasons"? If you splash some Factotum in there, you can get int to str & dex checks. Tome & potion & race, and that could be giving you another +6 to trips.

[Tancred]

Google-fu is weak

Try this: http://www.giantitp.com/forums/showthread.php?t=205001

[WinWin]

Tentacle Whip. (ECS). Symbiont. Price given in Magic of Eberron.