so, first off, this is just a non-exhaustive list on gear that you can use to replace any AGI gear with in 4.0. the criteria i have are anything that is easily attainable, either by using justice points, crafting, or a drop from 8/12 ICC (first wing, plague wing, dreamwalker). do note that this list is primarily aimed at people who are pugging their way through content, since any decent raider would already know this.
helmet: T10 helm, old triumph helmet, lady deathwhisper 10.
neck: deathwhisper25 neck, old conquest neck, putricide 10.
shoulders: BoE ICC shoulders, T10 shoulders, old triumph shoulders.
cloak: old frost cloak, gunship 10man, rotface 25man.
chest: T10 chest, old frost chest, marrowgar 25, ToC crafted.
bracers: ToC crafted, gunship 25, dreamwalker 10, halion 10.
gloves: T10 gloves, old frost gloves, festergut 25 and 10.
belt: old frost belt, dreamwalker 25, rotface 10.
pants: T10 pants, ICC crafted, dreamwalker 25.
boots: ICC crafted, deathwhisper 25, gunship 10, halion 25 (if your server can take it)
rings: ashen band of endless might, festergut 25, gunship 25, halion 10, rotface 10.
trinkets: old frost trinket, Halion 25 trinket, putricide 25, deathbringer 25, deathwhisper 10, greatness card.
this should provide you with ample opportunities to check and replace your AGI items you are using. personally, i'll need to replace a ring, my neck, my cloak and my boots. ring will be ashen band, neck will be putricide 10, cloak will be old frost cloak and boots will be crafted.