Utility to store/cache all web pages and YouTube videos

"I think MM3-WebAssistant does what you want. I haven't used it, but based on the web page (http://www.proxy-offline-browser.com/) it acts as a web proxy between your browser and the web. It automatically caches web pages and serves them from the cache when you're offline.
I'm not sure how it handles YouTube videos and it's garbage collection (cache clearing) is a bit of a mystery, but it is probably worth a shot."