ICAO Europe region documents
Amongst the real webcrawlers this might be known, but besides the ICAO Annexes there’s a lot more infomration available.
On this website you will find the ANP (Air Navigation plan) off the European ICAO region. A lot of specific information regarding ATC and navigational stuff in Europe. Pay also attention to the COM-tables which give a very complete view on the official released VHF frequencies (inclusief company). Also interesting is the whole SSR-allocation (the squawk codes) procedure. If you want to know the whole thing, also the important principle documents.