Vlad(/rake) task to let you know what you'd be deploying if you were to do so now...(based off your repo's 'origin' server master branch)

custom_vlad_tasks.rake

namespace :deploy do
    desc "Show which commits would be deployed right now"
    remote_task :what do
      print "(Locally) Fetching current state of origin..."
      `git fetch origin`
      origin_master_head = `cat .git/refs/remotes/origin/master`.chomp
      origin_head_details = `git log #{origin_master_head} --pretty=oneline -n 1`
      puts origin_master_head

      print "Current commit on server is..."
      production_head = run("cd #{deploy_to} > /dev/null 2>&1 && cat .git/refs/heads/master").chomp
      puts ""

      if origin_master_head == production_head
        puts "Server is in sync with origin/master...no need to deploy"
      else
        puts "If you deploy now, the following commits will be added to prod:"
        puts `git log #{production_head}..#{origin_master_head} --oneline  --abbrev-commit`
      end
    end
end

Use: rake deploy:what (or, rake production deploy:what if you use staged deploys)