Not plumbing, but I have these in my .gitconfig:
lsum = log -n 1 --pretty=format:'%s'
lmsg = log -n 1 --pretty=format:'%s%n%n%b'
That's "last summary" and "last message". You can provide a commit to get the summary or message of that commit. (I'm using 1.7.0.5 so don't have %B.)