Be sure to grab combat reflexes. You can substitute your attack of opportunity for a trip attack. This is one of the reasons that most trip fighters try to have some form of reach; either through their weapon, magic, race or some feat. The more ground you can control, the better. I don't know much about psychic warrior but you can always get potions of Enlarge Person pretty cheap. Or ask your GM if you can get a magic vest that does something similar.
Spiked Chain is sometimes considered the best tripping weapon. It has reach, but can also attack adjacent to you. However, it's an exotic weapon and you stated previously that you do not, or cannot, use an exotic weapon.
I prefer halberds. You can trip with it and set to receive a charge. If you can somehow get a pair of Steadfast Boots (Magic Item Compendium) you are always considered to be set to receive a charge. It's cheesy; allowing you essentially infinite readied actions each turn. If only you got advantages for pulling people off horseback....
Flails are another option. A normal flail would let you also use a shield. You could also branch into disarming with a flail. You would already have the pre-requisite feats for improved disarm. Combat Expertise feeds into both Improved Trip and Improved Disarm.
The guisarme can trip, has reach, but cannot attack foes adjacent to you. Invest in something like a spiked gauntlet so you can punch people in the face. Or, if you can convince your GM, pick up the feat Shorten Grip from Dragon Compendium. It lets you attack foes adjacent to you with a reach weapon but you take a -2 penalty to hit. You can also use Short Haft from Players Handbook 2 but that costs you your swift action instead of taking a penalty to hit.
Finally, the scythe can trip. The biggest appeal of this weapon is that sweet sweet x4 crit multiplier!
@Dannyalcatraz Knock-Down is in the 3.5 srd. But it looks like it was printed in Deities and Demigods and in Sword and Fist, both 3.0 books.
