I have a phone ringer I've used for years. Found it in an online sound effect archive and fixed it up a bit, extended it to 20 secs. It's a really basic telephone ringer, but it seems to be the only thing that will be guaranteed to get my attention.
Sadly, it also seems to be a very popular sound for use in TV commercials. Hardly a week goes by when I don't reach for my phone only to find that it was my TV ringing.