Polish:
PWN Encyclopedia and Dictionaries
Dictionary of Foreign Words and Phrases by Kopaliński
Thesaurus

German:
Tejo German-Polish Dictionary
German Linguistic Portal
Dict CC English-German Dictionary

French:
Tejo French-Polish Dictionary

Spanish:
Tejo Spanish-Polish Dictionary
English-Spanish Dictionary

Italian:
Tejo Italian-Polish Dictionary

Chemistry and Biology:
English-Polish Chemistry Dictionary
Chemistry Dictionary
ChemiCool Dictionary
Chemistry Glossary
Biology Dictionary
Biomedicine Dictionary

Finance:
English-Polish Financial Dictionary
Financial Glossary

IT:
Digipedia English-Polish Computer Dictionary
IDG English-Polish Computer Dictionary and Lexicon

Medicine and Pharmacy:
English-Polish Medical Dictionary
Tejo English-Polish Medical Dictionary
Multilingual Medical Dictionary
Dictionary of Medical Related Terminology
Medical Dictionary Online

Environmental Protection:
Multilingual Environmental Terminology Discovery Service
Glossary of Agri-environmental Terms

General:
Dict English-Polish Dictionary
Ling Multilingual Online Dictionary
Leksyka Online Dictionary
Ectaco Electronic Dictionaries
Megaslownik Multilingual Dictionary
Merriam-Webster Dictionary and Thesaurus
Global Glossary Multilingual Dictionary
YourDictionary Dictionary and Thesaurus
TheFreeDictionary English Dictionary and Encyclopedia
Cambridge Online Dictionaries
Dictionary.com English Dictionary, Thesaurus and Encyclopedia

Law:
Tejo English-Polish Law Dictionary
English Dictionary of Legal Terminology
Legal Glossary

Statistics:
Glossary of Statistical Terminology

EU Multilingual Term Base:
IATE Multilingual Terminology Base
Eurovoc Multilingual Thesaurus