Monitor 1st!
then...
GPU's
CPU
GPU
SSD
all cost 200-250 GBP
then some way down after that
Case
Ram
Blu-ray rw
Keyboard etc
Was the VDU worth it? Hell yeah! 2560x1600 will keep my gfx looking great during gaming for many moons to come. It's a god send when using Visual Studio/SSMS too!