why only 4GB ram? how long do you want to keep the system for? if it's longer than a year or 2, then why not go for 8GB from the start? Also, if you want to keep the system for a while it might be better to go for a quad core (Q6600).
also, for the monitor, why not go for a 1080p tv? you can get 40/42" LCD tv for £4-600
as for the GPU, if you have on already, i'd use that until june/july since iirc, that's when the new cards come our from ATi. If you dont want one of those, it would at least knock down the prices of other cards.