For the last 6 months my go-to site for Internet randomness has been PopUrls. I value a well done aggregator, and Magma takes the concept to the next level. Not only does it pull videos from across the web, it works in real-time so the freshness is near 100%. That, combined with filtering putting the best videos on the top, makes for a fantastic homepage experience.
I look forward to seeing the rollout of the social networking and measurement features, as well as how others take advantage of the API.