Sjors in the ##apple IRC chat room on Freenode came up with a simple script to find large files which are newer than your latest backup:

sudo find /Volumes/Data -newer /Volumes/BACKUPDRIVE/Backups.backupdb/smbp/2013-02-16-044144 -and -ls | awk '{ if ($7 > 1024*1024) {print $11 $12 $13 $14 $15 $16 } }'

/Volumes/Data = your primary drive which will be backed up.
/Volumes/BACKUPDRIVE = your mounted (USB, Firewire, etc) backup drive.
/2013-02-16-044144 = change to match the latest backup folder you see.