A simple Python script that lets you post to the notification center from the command line without dealing with a full desktop app. Because I can.

notification-center.py

#!/usr/bin/python

# Copyright (c) 2013 Adam Knight
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

import Foundation
import argparse, sys

args_parser = argparse.ArgumentParser()

args_parser.add_argument('-t', '--title', action='store', help="The title at the top of the notification (in bold)")
args_parser.add_argument('-s', '--subtitle', action='store', help="The subtitle just below the title")
args_parser.add_argument('-i', '--informative-text', action='store', help="Some longer text that appears in the body of the notification")

args = args_parser.parse_args()

if not args.title:
    args_parser.print_help()
    sys.exit(1)

nc = Foundation.NSUserNotificationCenter.defaultUserNotificationCenter()
n = Foundation.NSUserNotification.new()
n.setTitle_(args.title)
n.setSubtitle_(args.subtitle)
n.setInformativeText_(args.informative_text)
nc.deliverNotification_(n)