I would say most Browser based MMOS, such as Runescape. I like Guildwars and play wow, I have also played Warhammer online and have recentaly also tried out Starwars galaxies, they have something unique and better then the Browser based but none of the have that 'addictive flare' World of warcraft has, for its probably the indepth (im talking ocean depth not puddle) back story that has take 3 games and about 10 books to tell.