This is a Chrome extension that actually works from the Web Store—because it doesn't let you download YouTube videos. It time marks snippets you can share (only from YouTube). First create an account and log in. The extensions icon turns green on a YouTube page—click it to create the times you want, and they are then saved and easily shared; the viewer goes back to YouTube and sees what you specify. It's not really close to saving a video for your offline use, but could be useful in certain circumstances.
Have something to say about one of the contenders? Want to make the case for your personal favorite, even if it wasn't included in the list? Remember, the top five are based on your most popular nominations from the call for contenders thread from earlier in the week. Don't just complain about the top five, let us know what your preferred alternative is—and make your case for it—in the discussions below.
Another workaround: Go back to the desktop and try AnyTrans ($39.99 for a single computer), a file manager for iOS devices that has an integrated downloader supporting 900 sites, including YouTube and Facebook. It'll transfer the videos to the iPhone for you over the USB cable. Even if you don't pay for AnyTrans, the download option remains and is free forever.