Cloister's M:TG price guide.
CrystalKeep, large comprehensive M:TG database. (mirror, one file)
Dragonstudios mirror, home of Apprentice and Magic Suitcase.
MTG E-league mirror, for Apprentice updates and news.
Magic Set Editor for keeping your Apprentice sets up-to-date.
MTGNews, news on all MTG online gaming
Apprentice Hacks (cheating reference)
Backwash official site