Deffo build your own.. I was suprised how easy it was.
I built a system with an X blade case, 600GB storage.. 1GB Ram, 2.53GHZ processer (tho I would have liked to be able to afford more)
and extra fans and neon lights ect, and 2 DVD Burners for about £500.
And its perfect for my use.

Other then that check out Dell.