I've never been a fan of themed bedrooms and would much rather let the boys bedrooms evolve over time than go and by everything new and matching. My boys have always liked both star wars and Lego and although I'm sure they would love the curtains, duvet cover and lampshade here are a few more subtle suggestions.
An Ikea box frame and some very strong glue and you've got a bit of modern art!
A lot of patience
A fun wake up call from the dark side
Soft cushion for extra comfort on the bed
Do you like a themed room if so whats your theme?