Top political science databases
Political Science Complete (comprehensive, mostly full-text political science database)
Oxford Bibliographies Online: Political Science (annotated literature lists on a variety of topics in political science, compiled by specialists of the field)
Oxford Bibliographies Online:International Relations (as above but for international relations)
Oxford Research Encyclopedia Politics (encyclopedia delineating current research topics in all subfields, continuously updated and expanded)
Oxford Research Encyclopedia International Studies (as for International Studies, with rich international relations content)
Columbia International Affairs Online (CIAO) (international relations database published by Columbia University. Primarily recommended as a source for U.S. foreign affairs, with unpublished reports and papers from foreign policy think tanks)
wiso (the only German-language database on the subject; contains World Affairs Online sub-database and social sciences thesaurus).

Guidance through the publication maze
Literaturkompass Politikwissenschaft (introduction to key German and English literature from all subfields of the subject, from 2013; Springer publication, available online read-through and download)

Current issues of key e-journals at a glance
BrowZine Political Science (latest issue plus back issues of a wide selection of journals from all subfields of the discipline; full text from 2005 onward)

Statistics, country reports and indexes
OECD iLibrary (all OECD studies and statistics – one of the most far-ranging sources of data on global economics, society and the environment)
Compendium by U.S. political scientist Paul Hensel (covering key indices and datasets on international relations and conflict research, including on freedom of the press, human rights, governance and the quality of democracy)

Finding what I am looking for...
'Political Science: How do I find resources for my discipline?' (overview of pertinent information sources for anthropology)