I've bought many flashes drives from the 7 dayshop and they've always been reliable. I've not bought this particular type but 4GB seems to be the most economical size and these ones are relatively fast (135X) and should make ideal presents if you don't mind the branding, though you can probably remove it with a suitable solvent if you are fussy. AFAICT these are the cheapest 4GB drives around. Postage is free but slow particularly now with the postal strikes so I should order them soon if you want them before Christmas.
www.7dayshop.com/catalog/images/products/prod_106965_1.jpgg