Models, observations:

www.wetterzentrale.de/topkarten
www.meteociel.fr
www.infoclimat.fr
www.meteocentre.com
www.wetteronline.de
www.weatheronline.co.uk

Lightning data:

www.blitzortung.de
www.lightningmaps.org
http://cirrus.meteo.noa.gr/forecast/bolam/index.htm

Satellite images:

www.sat24.com
https://earthdata.nasa.gov/data/near-real-time-data/rapid-response/modis-subsets
eumetsat.com

Severe weather reports:

http://www.essl.org/cgi-bin/eswd/eswd.cgi
http://www.icwr.ca

Radar:

wetteronline.de (but I use the app)
http://europa.buienradar.nl/h.aspx?r=&jaar=-3&soort=loop1uur
http://www.aemet.es/es/eltiempo/observacion/radar
http://www.yr.no/place/Norway/Hordaland/Bergen/Bergen/radar.html
http://m.radareu.cz
http://radar.bourky.cz

Pages:

www.meteoweb.eu
youreporter.it
cazatormentas.net
wzforum.de
www.skywarn.de
http://www.skywarn.at
http://www.skywarn.org.uk
http://www.skywarn.eu etc
www.ukweatherworld.co.uk
http://uk.weather.com
http://www.sturmforum.ch
http://www.crometeo.hr
http://www.metoffice.gov.uk
 

Bushfires:

http://forest.jrc.ec.europa.eu/effis/