The Institute for European Politics (Berlin) website features an array of interesting studies and perspectives on European integration.
The best place to look for official and concise information on member states is the European Countries section of the EU’s official webpage, which offers information and statistics on all member and candidate states, as well as other European countries. Other useful links and up-to-date information surrounding EU policy and member states can also be found on the homepage of the European Commission.
For data on perspectives on the EU sorted by member states, refer to research done by the Pew Research Center here.