Do the expansions add much to it? I can play it for hours on end, but I've wondered if it's really worth paying for the add-ons.Saw your title and thought 'Civilisation IV' - seems a lot of others did too! I recently bought it, in a 'Complete' package which includes the Warlords and Beyond the Sword expansions as well. You could play that game for hours (i have), and it's a lot of fun.
If you don't play the scenarios, don't bother with Warlords as you'll get all the new units/buildings/etc from it in BtS as well. BtS adds a bunch of neat stuff mostly for the modern age including corporations (which act sort of like religion but provide bonuses/handicaps to city production based on available resources) and also greatly expanded espionage.