Where can I find a maintained proxy URL?

To improve my internet anonymity I've looked into using proxies. The issue I'm having is that as proxies come and go, it's difficult to locate proxy lists that are up-to-date and working. Most browsers will allow you to, rather than putting the proxies you want to use in manually, specify a URL that will hold a text file with your proxy chain - if that proxy list is updated, then you'll automatically start using the new proxies. I'm very interested in using that set-up, but can't find a proxy URL that's actually maintained anywhere. Does anyone know of one?