Good methods for denying dex bonus?

[Ridley's Cohort]

Well, the following "Conditions" are listed in the DMG as conditions that cause the creature to loose Dex to AC.

Blinded, Cowering, Flat-footed, Grappled, Helpless (Bound, Held, sleeping, paralyzed, unconcious, incapacitated), Stunned
(from DMG, condition summary section)

So any spells or tactics that you can find that will cause the target to have any of these conditions will cause him to loose his Dex to AC.

As a practical matter...

Invisibility makes your target effectively blinded to you. Holy Smite (and kindred spells) work nicely, too. Holy Smite is a great one because it is an AoE you can drop on top of your allies during a brawl (if they chose their alignment wisely).

Winning initiative makes him flatfooted.

Sound Burst or stunning fists will cause a stun effect.

I suppose you could get the Blind Fighting Feat and brawl in Deeper Darkness. That could be amusing.

 

[James McMurray]

I would say go with the ring of blinking. Blink is just too useful to ignore.