Rules
There is a +5 modifier to the base level requirement when transmuting a normal rare/unique to the exceptional item type. There is a +7 modifier when a rare or unique is upgraded from exceptional to elite.

Uniques
To convert a Normal Unique Armor to its Exceptional equivalent: Use a Shael, a Tal and a perfect Diamond in the Horadric Cube with the item you wish to transmute.
To convert a Normal Unique Weapon to its Exceptional equivalent: Use a Sol, a Ral and a perfect Emerald in the Horadric cube with the item you wish to transmute.
To convert an Exceptional Unique Armor to its Elite equivalent: Use a Lem, a Ko and a perfect Diamond in the Horadric cube with the item you wish to transmute.
To convert an Exceptional Unique Weapon to its Elite equivalent: Use a Lum, a Pul and a perfect Emerald in the Horadric cube with the item you wish to transmute.

Rares
To convert a Normal Rare armor to its Exceptional equivalent: Use a Thul, a Ral and a perfect Amethyst in the Horadric Cube with the item you wish to transmute.
To convert a Normal Rare weapon to its Exceptional equivalent: Use an Amn, an Ort and a perfect Sapphire in the Horadric Cube with the item you wish to transmute.
To convert an Exceptional Rare armor to its Elite equivalent: Use a Pul, a Ko and a perfect Amethyst in the Horadric Cube with the item you wish to transmute.
To convert an Exceptional Rare weapon to its Elite equivalent: Use an Um, a Fal and a perfect Sapphire in the Horadric Cube with the item you wish to transmute.

Recipes: https://diablo.fandom.com/wiki/Upgrading
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NORMAL UNIQUES --> EXCEPTIONAL

Goblin toe (x1 = str req 95, x2 = str req 163) - smiter? kicksin?
1 Tal Rune + 1 Shael Rune + 1 Perfect Diamond + Normal Unique Armor
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Goldwrap (x1 = yes, x2 = str req 151)
1 Tal Rune + 1 Shael Rune + 1 Perfect Diamond + Normal Unique Armor
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Magefist (x1 = yes, x2 = str req 151)
1 Tal Rune + 1 Shael Rune + 1 Perfect Diamond + Normal Unique Armor
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Bloodfists (x2 str req is 50)
1 Tal Rune + 1 Shael Rune + 1 Perfect Diamond + Normal Unique Armor

Tarnhelm (x2 str req is 84)
1 Tal Rune + 1 Shael Rune + 1 Perfect Diamond + Normal Unique Armor

Chance guards (x2 str req is 106)
1 Tal Rune + 1 Shael Rune + 1 Perfect Diamond + Normal Unique Armor
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Bonesnap (can be fun)
1 Sol Rune + 1 Ral Rune + Perfect Emerald + Normal Unique Weapon

Rixot's Keen (can be fun)
1 Sol Rune + 1 Ral Rune + Perfect Emerald + Normal Unique Weapon

Chieftain axe (x1, str req is 101 [tabar])
1 Sol Rune + 1 Ral Rune + Perfect Emerald + Normal Unique Weapon


EXCEPTIONAL UNIQUES --> ELITE

Titans (obviously)
1 Lum + 1 Pul + 1 Perfect Emerald + Exceptional Unique Weapon

Skin of the vipermagi (definitely - can go from ~280 def to ~970 def)
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Herald of Zakarum (no - str req goes from 89 to 142 - RIP)
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Gore riders (no - x1 and str req is 156 - RIP)
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Arreats
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Skullder's Ire (eh - str req is 165? [balrog skin])
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Shaftstop
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Duriel's Shell (definitely - str req is only 108)
1 Ko Rune + 1 Lem Rune + 1 Perfect Diamond + Exceptional Unique Armor

Ginther's Rift
1 Lum + 1 Pul + 1 Perfect Emerald + Exceptional Unique Weapon

Eth merc weapons (like kelpie)

Any decent rares

Any good rare eth crystal swords or dimensional blades... these are the only way to get a GG rare phase blade.