First, Power attack as far as i am aware of is actually an anti Trip feat.
Second, you need to give an example of your level and your current CMB. I would then suggest going through the Beastiary and checking your chance of tripping monsters at your own CR.
A general thing though is, things with lots of legs are hard to trip, things that are large are hard to trip and finally, things that have Magic Bonuses to Ac that are not armor bonuses are hard to trip.
So what was the bad guy you were facing?
Anything that improves your attack.
Weapon focus, smite evil, favorite enemy, weapon enhacement, flanking, higher ground - they all add
Cracked pale green prism Ioun stone
Way finder + dusty rose Ioun stone
Gloves of dueling (in case you are a fighter)
Gauntelts of skilled maneuvers
Ask for buff from your party. Bless, haste, whatever that give you a bonus to attack give you a bonus to your CMB for trip.
And lastly, the single handely most CMB increasing item is the dueling (from the field guide) weapon enhacement for weapons.
Heh, ya, increasing your CMB isn't hard. Now, increasing your CMD, that's a pain.
Anything that improves your attack.
Weapon focus, smite evil, favorite enemy, weapon enhacement, flanking, higher ground - they all add
I thought your CMB was BAB+(Strength Bonus) Only?
No.
When you attempt to perform a combat maneuver, make an attack roll and add your CMB in place of your normal attack bonus. Add any bonuses you currently have on attack rolls due to spells, feats, and other effects. These bonuses must be applicable to the weapon or attack used to perform the maneuver. The DC of this maneuver is your target's Combat Maneuver Defense. Combat maneuvers are attack rolls, so you must roll for concealment and take any other penalties that would normally apply to an attack roll.
http://www.d20pfsrd.com/gamemastering/combat#TOC-Combat-Maneuver-Bonus
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Disarm, sunder, and trip are normally the only kinds of combat maneuvers in which you’re actually using a weapon (natural weapons and unarmed strikes are considered weapons for this purpose) to perform the maneuver, and therefore the weapon’s bonuses (enhancement bonuses, feats such as Weapon Focus, fighter weapon training, and so on) apply to the rol
http://paizo.com/paizo/blog/v5748dyo5lcom
I'm a Anti-Paladin level 13, CMB +19 (+23 for Trip)
That isn't very good for a dedicated tripper at level 13.
13 from bab.
Should have 5-7 from str.
Then another 1 from focus. 4 from greater trip. 3-4 from weapon enchantment.
Some way to get bigger, for more Str and another CMB boost, plus being able to trip bigger stuff.
Maybe a +30-35 or so. And that is without really min/maxing for the best trip check out there.