The first things that springs to mind are filters.
Square ones are the way to go for a number of reasons, mainly flexibility of use and you can use them on almost all your lenses. An affordable range at the Hi-tech's, i own a couple of cokin's and while being very cheap, they aren't great (they can give the photo a strong colour cast)
Anyway, the way it works is you buy a filter holder:
here
And an adapter ring:
here The ring attaches the holder to the lens, i've linked you to a 58mm one because that will fit the standard lens that comes with the 1000D, but the idea is, if he has or gets lenses which have a thread larger than 58mm, then you just buy another ring, for £12, rather than a whole new set of filters.
Then you get whatever type of filter you want and slide them into the holder:
here
Regarding your choice of filters, the graduated ND kits or a couple of the plain ND's would be good and cokin does a large range of special effects and coloured ones which are fun to play with and might be good for cityscapes.
p.s chaz has made some good suggestions as well