Copying to external USB 2.0 drive hangs

I have had problems copying files to my external USB 2.0 hard drive. My initial testing shows that if my file copy is very large (2GB or more), OS X will simply stop copying, though the progress bar suggests it is still going. The progress bar just sits there idling, with the promise of copying more but it never does. I have to restart the computer to get it to forget about the file copy. Hitting the cancel (grey "X") button in the copy dialog box does nothing. System Profiler says it sees the drive. The external drive shows no activity during this.
The Finder hangs and I have to restart the system to get a usable computer again.

I'll need to do more thorough testing with the other USB ports and alternate cables, but I was wondering if anyone has experienced anything similar.