http://www.roofbox.co.uk/ for loads of them and info.
Bought this one
http://www.roofbox.co.uk/scripts/rbv...e=boxgen&qty=1 'cos it didn't require selling a kidney to fund (unlike some...) but at the same time looked sturdy enough not to have to dodge lorries on French autoroutes picking up suitcases...
Ended up being a good buy and worth the money.
Company were good to deal with. Fast delivery, 90 day exchange policy and helpful when the roof bar manufacturers screwed up and supplied 3 wrong feet for the roofbars.