These are my favorite sites:

Wizards of the Coast : The official Magic the Gathering site
MtGNews : Probably the best site about Magic...
Yavapai Open : Here you can find pictures of every single magic card...
Dojo : Used to be better but I still like it...
Slovak site : Used to be good, but I don't know what happened.
Czech site : Much much better than our Slovak one.
D'Angelo's site : Here you can find latest rulings and erratas and many more.