Well, if you have a PPC running Tiger or older, there's always the option of running Disk Copy under Classic. (And if you are running 10.2 or older, you get an actual OS X-native version of Disk Copy.)

In OS X 10.3+ proper, there is Disk Utility. I don't know about cross-compatibility between Disk Utility and Disk Copy, though. (And Disk Utility imaging is the only way to "format" a floppy disk as HFS in later versions of OS X. You take a blank HFS disk, image it, then write the image out to another disk.)

I believe DMGConverter can convert between Disk Utility and Disk Copy formats, but I'm not positive.