you can't add a link outside youtube with the annotation. But you can add a link to another video. For each money video that you have, upload couple video to support it. Like 1 money video with 20 sexy video to generate it traffic using annotation/description. Just use a catchy keyword, and make people want to click your link. It will increase your money video view and rank too. You'll get backlink for better search rank and view. Do it smart, if the 20 videos stay forever, you'll get steady traffic to your money video for free forever too. If you still need more view, just add more sexy video. Once it reach high rank and get organic traffic, you can direct the traffic to your other money video. Spin your own web to catch that flying $$$.