Just reading this thread and wanted to say I've had some good reliable long term success with proxic (search for proxic 1.03) by nullox and I only use this now, it has an algorithm which attempts to extract proxies from many lists which I've found is quite reliable, just input list URLs which it can save for later polling and let it pull em.
If you purchase the app, a preleech list exists which is maintained by the developers, however you can use your own which is perhaps better and without a license, you are only limited to 1k results which is often enough.