netcheck.py

#!/usr/bin/python
# -*- coding: UTF-8 -*-
import urllib2
import appindicator
import pynotify
import gtk
from concurrent import futures
import socket

class Checker:

    last_check = True
    a = None

    def internet_on(self):
        try:
            response=urllib2.urlopen('http://74.125.228.100',timeout=2)
            return True
        except urllib2.URLError as err: pass
        except socket.timeout as err: pass
        return False

    def quit(self, item):
        gtk.main_quit();

    def check(self):
        current_check = self.internet_on()
        if self.last_check != current_check:
            self.last_check = current_check
            pynotify.init('netcheckindicator')
            if current_check:
                body = 'Van internetkapcsolat'
                self.a.set_icon('ubuntuone-client-idle')
            else:
                body = 'Nincs internetkapcsolat'
                self.a.set_icon('ubuntuone-client-error')
            n = pynotify.Notification('Internetkapcsolat ellenőrző',
                    body,
                    'network')
            n.show()
        gtk.timeout_add(3000, self.check)

    def main(self):
        # print what
        self.a = appindicator.Indicator('netcheckindicator', 'ubuntuone-client-idle', appindicator.CATEGORY_APPLICATION_STATUS)
        self.a.set_status( appindicator.STATUS_ACTIVE )
        m = gtk.Menu()
        mQuit = gtk.MenuItem('Kilépés')
        mQuit.show()
        mQuit.connect('activate', self.quit)
        m.append(mQuit)
        self.a.set_menu(m)

        gtk.timeout_add(3000, self.check)
        gtk.main()

checker = Checker()
checker.main()

Threw together in 10 minutes, because my ISP (T-Home) is a dick, and my internet connection is totally unreliable. Does nothing else, but show an indicator on my Ubuntu 13.10 installation, and notifies me, if internet access is shut down, or is available again.