I have four working USB flash drives, the two largest ones a IGB and 4GB USB v.2.0 both produce occasional copy failed messages but are reliable once the data is on them. My two 100% reliable ones are both old, small, 32MB and 128MB, USB v.1.0.
I was very lucky to find.
I've used all four with a range of Xbox versions, 1.0, 1.1, 1.2 and three 1.6s and had no problem with any of them.
All I can tell you is to search out some of old threads on this oft discussed subject. There is also that wiki list you can find by Googling but it is mostly old and can't be relied on. As spliff721 says it really is hit or miss.