What’s Trending
http://whatstrending.com/
Google Trends
http://www.google.com/trends/

Twitter / Trends
https://mobile.twitter.com/trends

Trending on Instagram
http://www.oninstagram.com/trending

Top Hashtags
http://top-hashtags.com/

http://top-hashtags.com/instagram/

Twitter Search
https://twitter.com/search–home

YouTube Trends Dashboard – YouTube
https://www.youtube.com/trendsdashboard

Finding Popular Conversations on Facebook
http://newsroom.fb.com/news/2014/01/finding-popular-conversations-on-facebook/