I was digging around the gdb source and found that there's a plugin in there that supports macsbug style screens and commands from within gdb. If you have the XCode Tools installed, take a look at the Readme on your own (OS X) system at the file /usr/libexec/gdb/plugins/MacsBug/Readme.html
To invoke it, type this at the GDB prompt:
and you've got the old split screen with the register contents on the left.
I never used macsbug for anything real, but this still held some nostalgic value.