X-ray astronomy

SRON Netherlands Institute for Space Research
http://www.sron.nl/

Conference High-Resolution X-ray Spectroscopy: past, present, and future
http://www.sron.nl/xray2010

SPEX X-ray Spectral Fitting Package
http://www.sron.nl/spex

XMM-Newton on the ESA website
http://www.esa.int/science/xmmnewton

Popular astronomy

Public Observatory "Philippus Lansbergen"
http://www.lansbergen.net/

Jelle de Plaa (Popular Astronomy and photography site)
http://www.deplaa.net/