This is actually quite simple. And FREE. I'm going to assume you're using Firefox as your browser. If not, you'll need to for this.Get it free at www.mozilla.com. With Firefox open, click the "Tools" menu at the top. When the menu opens, click on "Add-ons". When the Add-ons window pops up, click on the icon at the top that says "Get Add-ons". On the right side there should be a link that says "Browse All Add-ons". Click it. That will open a new page that says "Add-ons for Firefox". There will be search box that says "search for add-ons". Type in "video downloadhelper" (make sure its "downloadhelper" all one word, not download helper) in the search. It should be the first result that comes up. Click the "Add to Firefox" button. Install it, and restart Firefox. When a site has a video you can download, you will notice a small rotating icon of a red, yellow, and blue balloon next to your address bar. Click the icon, select the video you want, and download away! Video downloadhelper works with YouTube and TONS of other sites too. There are some sites (like Hulu) that won't let you download the videos, but most will. Video downloadhelper has worked GREAT for me!
My own personal experience. Had the same problem. Now I can download vids from YouTube all day!