I often found my self to fill in table rates for Magento shipping method, and got errors as I inserted the wrong codes.

Here an useful table containing all the codes.

I would suggest to download the CSV file from Magento to make sure you have the right format.

Enjoy.

Country | 2 Digit Code | 3 Digit Code
Afghanistan | AF |  AFG
Albania | AL |  ALB
Algeria | DZ |  DZA
American Samoa | AS |  ASM
Andorra | AD |  AND
Angola | AO |  AGO
Anguilla | AI |  AIA
Antarctica | AQ |  ATA
Antigua and Barbuda | AG |  ATG
Argentina | AR |  ARG
Armenia | AM |  ARM
Aruba | AW |  ABW
Australia | AU |  AUS
Austria | AT |  AUT
Azerbaijan | AZ |  AZE
Bahamas | BS |  BHS
Bahrain | BH |  BHR
Bangladesh | BD |  BGD
Barbados | BB |  BRB
Belarus | BY |  BLR
Belgium | BE |  BEL
Belize | BZ |  BLZ
Benin | BJ |  BEN
Bermuda | BM |  BMU
Bhutan | BT |  BTN
Bolivia | BO |  BOL
Bosnia and Herzegovina | BA |  BIH
Botswana | BW |  BWA
Bouvet Island | BV |  BVT
Brazil | BR |  BRA
British Indian Ocean Territory | IO |  IOT
British Virgin Islands | VG |  VGB
Brunei | BN |  BRN
Bulgaria | BG |  BGR
Burkina Faso | BF |  BFA
Burundi | BI |  BDI
Cambodia | KH |  KHM
Cameroon | CM |  CMR
Canada | CA |  CAN
Cape Verde | CV |  CPV
Cayman Islands | KY |  CYM
Central African Republic | CF |  CAF
Chad | TD |  TCD
Chile | CL |  CHL
China | CN |  CHN
Christmas Island | CX |  CXR
Cocos [Keeling] Islands | CC |  CCK
Colombia | CO |  COL
Comoros | KM |  COM
Congo | CG |  COG
Congo | CD |  COD
Cook Islands | CK |  COK
Costa Rica | CR |  CRI
Croatia | HR |  HRV
Cuba | CU |  CUB
Cyprus | CY |  CYP
Czech Republic | CZ |  CZE
Côte d’Ivoire | CI |  CIV
Denmark | DK |  DNK
Djibouti | DJ |  DJI
Dominica | DM |  DMA
Dominican Republic | DO |  DOM
Ecuador | EC |  ECU
Egypt | EG |  EGY
El Salvador | SV |  SLV
Equatorial Guinea | GQ |  GNQ
Eritrea | ER |  ERI
Estonia | EE |  EST
Ethiopia | ET |  ETH
Falkland Islands | FK |  FLK
Faroe Islands | FO |  FRO
Fiji | FJ |  FJI
Finland | FI |  FIN
France | FR |  FRA
French Guiana | GF |  GUF
French Polynesia | PF |  PYF
French Southern Territories | TF |  ATF
Gabon | GA |  GAB
Gambia | GM |  GMB
Georgia | GE |  GEO
Germany | DE |  DEU
Ghana | GH |  GHA
Gibraltar | GI |  GIB
Greece | GR |  GRC
Greenland | GL |  GRL
Grenada | GD |  GRD
Guadeloupe | GP |  GLP
Guam | GU |  GUM
Guatemala | GT |  GTM
Guernsey | GG |  GGY
Guinea | GN |  GIN
Guinea | GW |  GNB
Guyana | GY |  GUY
Haiti | HT |  HTI
Heard Island and McDonald Islands | HM |  HMD
Honduras | HN |  HND
Hong Kong SAR China | HK |  HKG
Hungary | HU |  HUN
Iceland | IS |  ISL
India | IN |  IND
Indonesia | ID |  IDN
Iran | IR |  IRN
Iraq | IQ |  IRQ
Ireland | IE |  IRL
Isle of Man | IM |  IMN
Israel | IL |  ISR
Italy | IT |  ITA
Jamaica | JM |  JAM
Japan | JP |  JPN
Jersey | JE |  JEY
Jordan | JO |  JOR
Kazakhstan | KZ |  KAZ
Kenya | KE |  KEN
Kiribati | KI |  KIR
Kuwait | KW |  KWT
Kyrgyzstan | KG |  KGZ
Laos | LA |  LAO
Latvia | LV |  LVA
Lebanon | LB |  LBN
Lesotho | LS |  LSO
Liberia | LR |  LBR
Libya | LY |  LBY
Liechtenstein | LI |  LIE
Lithuania | LT |  LTU
Luxembourg | LU |  LUX
Macau SAR China | MO |  MAC
Macedonia | MK |  MKD
Madagascar | MG |  MDG
Malawi | MW |  MWI
Malaysia | MY |  MYS
Maldives | MV |  MDV
Mali | ML |  MLI
Malta | MT |  MLT
Marshall Islands | MH |  MHL
Martinique | MQ |  MTQ
Mauritania | MR |  MRT
Mauritius | MU |  MUS
Mayotte | YT |  MYT
Mexico | MX |  MEX
Micronesia | FM |  FSM
Moldova | MD |  MDA
Monaco | MC |  MCO
Mongolia | MN |  MNG
Montenegro | ME |  MNE
Montserrat | MS |  MSR
Morocco | MA |  MAR
Mozambique | MZ |  MOZ
Myanmar [Burma] | MM |  MMR
Namibia | NA |  NAM
Nauru | NR |  NRU
Nepal | NP |  NPL
Netherlands | NL |  NLD
Netherlands Antilles | AN |  ANT
New Caledonia | NC |  NCL
New Zealand | NZ |  NZL
Nicaragua | NI |  NIC
Niger | NE |  NER
Nigeria | NG |  NGA
Niue | NU |  NIU
Norfolk Island | NF |  NFK
North Korea | KP |  PRK
Northern Mariana Islands | MP |  MNP
Norway | NO |  NOR
Oman | OM |  OMN
Pakistan | PK |  PAK
Palau | PW |  PLW
Palestinian Territories | PS |  PSE
Panama | PA |  PAN
Papua New Guinea | PG |  PNG
Paraguay | PY |  PRY
Peru | PE |  PER
Philippines | PH |  PHL
Pitcairn Islands | PN |  PCN
Poland | PL |  POL
Portugal | PT |  PRT
Puerto Rico | PR |  PRI
Qatar | QA |  QAT
Romania | RO |  ROU
Russia | RU |  RUS
Rwanda | RW |  RWA
Réunion | RE |  REU
Saint Barthélemy | BL |  BLM
Saint Helena | SH |  SHN
Saint Kitts and Nevis | KN |  KNA
Saint Lucia | LC |  LCA
Saint Martin | MF |  MAF
Saint Pierre and Miquelon | PM |  SPM
Saint Vincent and the Grenadines | VC |  VCT
Samoa | WS |  WSM
San Marino | SM |  SMR
Saudi Arabia | SA |  SAU
Senegal | SN |  SEN
Serbia | RS |  SRB
Seychelles | SC |  SYC
Sierra Leone | SL |  SLE
Singapore | SG |  SGP
Slovakia | SK |  SVK
Slovenia | SI |  SVN
Solomon Islands | SB |  SLB
Somalia | SO |  SOM
South Africa | ZA |  ZAF
South Georgia and the South Sandwich Islands | GS |  SGS
South Korea | KR |  KOR
Spain | ES |  ESP
Sri Lanka | LK |  LKA
Sudan | SD |  SDN
Suriname | SR |  SUR
Svalbard and Jan Mayen | SJ |  SJM
Swaziland | SZ |  SWZ
Sweden | SE |  SWE
Switzerland | CH |  CHE
Syria | SY |  SYR
São Tomé and Príncipe | ST |  STP
Taiwan | TW |  TWN
Tajikistan | TJ |  TJK
Tanzania | TZ |  TZA
Thailand | TH |  THA
Timor | TL |  TLS
Togo | TG |  TGO
Tokelau | TK |  TKL
Tonga | TO |  TON
Trinidad and Tobago | TT |  TTO
Tunisia | TN |  TUN
Turkey | TR |  TUR
Turkmenistan | TM |  TKM
Turks and Caicos Islands | TC |  TCA
Tuvalu | TV |  TUV
U.S. Minor Outlying Islands | UM |  UMI
U.S. Virgin Islands | VI |  VIR
Uganda | UG |  UGA
Ukraine | UA |  UKR
United Arab Emirates | AE |  ARE
United Kingdom | GB |  GBR
United States | US |  USA
Uruguay | UY |  URY
Uzbekistan | UZ |  UZB
Vanuatu | VU |  VUT
Vatican City | VA |  VAT
Venezuela | VE |  VEN
Vietnam | VN |  VNM
Wallis and Futuna | WF |  WLF
Western Sahara | EH |  ESH
Yemen | YE |  YEM
Zambia | ZM |  ZMB
Zimbabwe | ZW |  ZWE
Åland Islands | AX |  ALA