Posting on two social media sites
Stumbleupon works little different than Reddit but still it gets an amazing amount of traffic daily. If your video is good and liked by the Stumbleupon community it can go viral. If not, it is still a valuable backlink in your SEO efforts.
Yes, I can get you large amounts of traffic for a short period of time, but with the SEO backlinks I will get for your video, the effects can be long-term and they will help your video to rank better on YouTube.