In line with the other recent posts about online games (Eve, World of Warcraft, etc)...
Those whom like RPGs, like Diablo, might be interested in Guild Wars.
It's an online game with elements of MMO gameplay, but with a focus on small-group instanced quests/explorable areas and PvP playing.
Infact, the only places you'll see more than the people whom are in your 'party' (which can range from none - upto about 8 so far) are in public areas or Player vs Player areas, where you'll be opposing one or more other groups at a time.
Guild Wars is in closed 'alpha' testing at the moment, and up until recently had semi-open "Beta Weekend Events", once per month for those whom had pre-ordered, or gained a once-off access key.
Full Release is scheduled for April 28th, but there's plenty of info and community stuff happening.
Official Site: http://www.guildwars.com
Fairly well set-up GW Community Site: http://www.gwonline.net/
One of the more recent reviews: http://rpg.boomtown.net/en_uk/articles/ ... hp?id=7437
and ofcourse, the obligatory plug for ANZAC - the Guild Wars guild that I'm in --- http://www.anzgw.com/
Oh, and before I forget -- it looks real purdy too.