Promoting our own site:
http://www.theeuropeanlibrary.org

We are aggregating bibliographic records from 48 European national
libraries, major research libraries and some other free sources. We
also feature some special exhibitions, full text content and some
federated search for those collections that cannot be harvested.

It is a complete in-house development,Java/Solr based, from
aggregation and processing framework to frontend, using Apache Wicket.

Regards,
Rene Wiermer