Flash drives are a great solution for backing up or transferring files IF you can find one when you need it. It seems like no matter how hard I try, I just can't seem to keep one in my pocket all the time. They aren't particularly bulky or heavy, I just forget to put it in my pocket all the time. That is where LaCie's Iamakey flash drive wins hands down! The Iamakey is not much thicker than a regular key, fits on my keychain and its solid, metal case is durable enough to live in my pocket all the time with my keys. I love this solution. It is a bit more expensive that other drives, but the convenience is worth it to me. It comes in 4GB, 8GB and 16GB models that range from $22 to $55 respectively. Now, if I have my keys in my pocket, which I ALWAYS do, my flash drive is ready to go.
Check out the Iamakey - it will be the only flash drive I buy from now on.