Have your buddy take
Improved Precise Shot and
Fling Ally?
Rapier of Unerring Direction (MIC-55)
Revelation Crystal (MIC-66) - this is a bit tricky, since first the concealed creature needs to be hit, and it then cancels the concealment for 1 round
Bracers of Accuracy (MIC-79) - ignore miss chance, but not from TOTAL concealment
Crystal Mask of Visual Insight (MIC-92) - ignore concealment, but not from invisibility
Pierce Magical Concealment (CArc-81) - feat, disregard miss chance that's a result of a spell or SLA, such as Blur or Invisibility. Doesn't help vs non-magical concealment. Doesn't mention SU concealment, but I assume not.
Faerie Fire (PHB-229) - outlined creatures do not benefit from concealment from darkness, though concealment from 2nd-level or higher spells still apply
See Invisibility (PHB-275) - see invisible & ethereal targets, doesn't help with other concealment
True Seeing (PHB-296) - will allow you to see through some concealment such as blur or invisibility; won't help some other kinds of concealment (though a RAW arguement would say it doesn't even help vs blur & invisibility)
True Strike (PHB-296) - not affected by miss chance
Corpse Candle (CArc, SpC) - incorporeal & invis creatures no longer benefit from concealment
Fire Eyes (Masters of the Wild, a 3.0 book) - ignore concealment from normal smoke, fire, and fog. Does not help vs magical versions.
Heartfire (SpC) - outlined creatures do not benefit from concealment, although 3rd level spells still provide it
Illusion Purge (Races of Eberron) - negate illusions of 7th level or lower.
Mark of the Hunter (CDiv, SpC) - only vs a favored enemy
Shroud of Flame (SpC) - negates any concealment the target may have
Blindsight (DMG-290) - makes concealment irrelevant
(note that Blindsense (DMG-291) doesn't help
Scent (DMG-298) - maybe? There's a line near the end of DMG-295, talking about invisiblity, that says
A creature with the scent ability (page 298) can detect an invisible
creature as it would a visible one.
but actually looking at the scent ability, it merely says it can "pinpoint" the creature and doesn't mention negating concealment. We've played it does, but it hasn't come up a lot.
Good luck!