It is an incomplete list at present. Right now it only contains surface areas, though we may update it for Underdark areas at some point if possible.
Note that the CRs are based on the idea that you'll be taking the map on with a party. If you're going in solo, it's been suggested you add 2-3 levels to the area's challenge rating.
Valefort wrote:[The] stated CR [of some areas] is quite wildly different from the real difficulty. [Here] is a list of the CR on a bunch of surface areas, sorted by CR (I don't know anything about Underdark so I skipped it).
Soubar well : CR 0.5
East Chionthar : CR 1
BG, graveyard : CR 1.5
BG, graveyard cave : CR 2
Soubar ruins : CR 2
Kobolds : CR 2
Bladelings : CR 2.5
BG, east gate sewers : CR 2.5
Trade Way, south of BG : CR 2.5
Soubar, Bane temple : CR 2.5
Boareskyr Bridge bears : CR 3
Gibberling : CR 3
East Chionthar ruins : CR 3
BG, palace's district sewers : CR 4
East cloakwood : CR 4
Boareskyr : CR 4
Lion's way : CR 5-6
Ant burrow : CR 6
North of Beregost, goblins : CR 6
Cloakwood mine, level 1-2-3 : CR 6
Ulgoth's island : CR 6
Goblin mine : CR 7
Thundar's Ride : CR 7
Bridgefort : CR 7
BG, sewer bowels : CR 8
High Hedge : CR 8
Sharp Teeth : CR 8
Lion's way gnolls : CR 8
Cloakwood central : CR 8
Dragonspear exterior and castle : CR 9
Minotaurs : CR 10
BG, Undercity : CR 10
Hags : CR 12
North-west Cloakwood : CR 12
Chionthar, west : CR 12
Uldoon's trail : CR 13
Haunted house, level 1 : CR 13
Skuldaask's cave : CR 13
Haunted house, level 2 : CR 14
High Moor south : CR 14
Ulgoth's pirate : CR 14
Xvarts : CR 14
Fields of the dead : CR 14 on average
Elder Ogre stronghold : CR 15
Misty forest : CR 15
Gullykin crypt : CR 15
South of Beregost : CR 15
Fields of the dead, crypt : CR 15-16
Ulcaster : CR 16 (yes 16)
Ogre cave : CR 16
Corm Orp : CR 16
Durlag's exterior : CR 16
Durlag's tower : CR 16
Nashkel foothills : CR 16
Nashkel's mine exterior : CR 16-17
Troll Claws : CR 18 on average
Durlag's labyrinth 1-2 : CR 19
Nashkel's mine : CR 19
Cloud peaks : CR 19
Troll cave : CR 20
Yuan-ti hills : CR 20
Searing tunnels and searing caverns : CR 21
Haunted house, level 3 : CR 21
Ice cave : CR 22
Durlag's labyrinth 3 : CR 22
Spirit troll cave : CR 23
Wyrm's cave : CR 23
Yuan-ti temple : CR 23
Reaching woods : CR 23
Lizard cave : CR 23
Stone giants : CR 24
Vault, level 1 : CR 24
Forest of Wyrms : CR 24
Vault, level 2 : CR 25
Frost giants : CR 27
Graypeaks : CR 27
Speartop : CR 28
Vault, level 3 : CR 29
Netherese maze : CR 29
Distribution :
Level 0-5 areas : 16
Level 5-10 areas : 16
Level 10-15 areas : 15
Level 15-20 areas : 14
Level 20-25 areas : 13
Level 25-30 areas : 5