I am attending a birthday party for a friends son, age 15, who is very interested in things like Star Wars, Star Trek, old science fiction movies and programs, aliens and such.  I have no idea what type of gift to purchase as I know nothing of this type of thing.  Can anyone give me any good ideas please :)

Hmm. How about boxed sets of the films or something? You'd have to check with your friend which he has already though! Or there are some games based on Star Trek and Lord of the Rings and that sort of thing?

15 is a difficult age - not only to be, but to buy presents for!

I would suggest something gadgety - the problem being that the Gadget Shop has now closed down.  How about a 'leatherman' style multi-tool?  Not necessarily the genuine article, but you can get them for a reasonable price.

Cineme vouchers and a tub of popcorn are another good idea for boys.  Both the above are presents mine loved (I've just asked!).

What about a one year subscription to a sci-fi magazine. 

What about an original star wars or similar toy, from say the 70s. Many are becoming collectors items they are not yet too expensive to buy and since he wasnt around in the 70s it will be of novelty value too.

Why don't you have a look on E Bay, they have loads of things like that.

thanks for the great ideas, will have a look on Ebay right away :)