You can get fairly large lists from cspy.org (I see roughly a 20-30% success rate)
And i wrote a simple proxy checker earlier today that you can use to check them. (it is similar to the one at samair, but not limited at 50 per run, and is hostedon your server)
hxxp://blog.i3lackspace.com/archives/7
If there is a lot of interest in it, i will write a new (faster, multi-threaded) one that scrapes and checks.