Thanks all, some good suggestions there.
I like the iomega micro mini drive, think it's a rebadged pretec tiny which I'd seen before and which sparked this (deeply researched) impulse buy, but apparently the write speed (on the pretec at least) is noticeably slower than 'full-size' drives and it's a bit expensive too. Also considered a Sandisk Titanium 512Mb for ~£30, retractable drive, actually is made of titanium and supposedly is indestructable, but thought that it was a bit big (7.5cm). So taking the bytestor from amazon as a yardstick I ended up buying a sandisk cruzer mini for £22 delivered, figuring the extra £4 is worth it because it is only 5cm long and it has a VERY BRIGHT blue LED