Hard Disk Toolkit MAY work
HD Toolkit offers non-destructive HFS (and HFS+ I think) resizing, but I've never tried it. I'd be afraid of it screwing up file permissions as will have to move things around on the volume. (Although, if it's just moving the bits around, it should be as safe as Norton Speed Disk)
As others said, nothing exists for doing it from OS X as far as any of us know. (You wouldn't be able to do it to a drive that you're booted to anyway)