My favourite sites are:

http://www.luxforum.lu - the only real Luxembourgish forum on the net!

http://www.deviantart.com - very big artist community

http://www.photogen.lu - luxembourgish photo community!

http://www.larepublique.de - freaky German community!

http://www.wulfmorgenthaler.com - the best comics on the planet!

and many more…