I'm a gamer and probobly going to upgrade the GPU when something really good comes out.
well it would be good to have 30amp on 12v rails and max 600watts unless you do SLI or CrossfireX for more than 2 gpus.
Rest you can simply calculate from the site i already mentioned with upgrades in consideration.
Dont forget that a good psu with 600watts should cater any future needs unless you buy any cheap quality where you can avoid
any problems by having a higher power rating.