To download most of these porn videos you may use Replay Media Catcher.

See the following threads for more:
www.pornhub.com - Record XXX videos from flash player (http:// .flv)
Can not grab media from pornrabbit.com (Downloading rtmp:// .flv video stream)
www.xvideos.com - How to capture porn videos from Adobe Flash Player (http:// .mp4)
www.youporn.com - How to download free flash sex videos from You Porn (http:// flv)
www.shufuni.com: Can't download free amateur porn/sex videos from shufuni (rtmp .flv)
www.tube8.com: HowTo capture/download sex/porno videos without registering(HTTP .flv)
RedTube.com: How to download free flash xxx/porno/sex videos from RedTube (http .flv)
www.keezmovies.com: How to capture free porn tube movies from Keez Movies (http .flv)
www.spankwire.com: How to save free porn tube videos from Spank Wire (http:// .flv)
www.yazum.com: How to record rtmp .flv adult/sex/porn streaming videos from Yazum?