Ghostlight candle has a daily power that creatures within 2 lose insubstantial
Ghoststrike oil can let you ignore insubstantial on the next attack you make against an undead creature, if you hit with the secondary attack from the oil. (Frankly, this is a pretty terrible item.)
Orb of ghostbane triumph lets you ignore insubstantial as long as you have at least 1 power point.
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Ghost Touched (feat) + magic missile = ignore insubstantial.
Spectral Reaping (feat) + dark reaping (revenant power) = ignore insubstantial.
Penetrating Power (feat) lets you ignore all resistances, including insub, with your next attack. You have to be a controller to take the feat, though.
Untraceable Flurry (feat) + flurry of blows = ignore insubstantial. Requires the Elan Bloodline feat.
Inescacable Force (feat) + power with force keyword = full damage against insub +1d10 damage.