What’s HOT in search? 搜索引擎类：

• Google hottest trends (updates throughout the day);
• Yahoo buzz allows to see the daily buzz score (=”the percentage of Yahoo! users searching for that subject multiplied by a constant to make the number easier to read“) and the move(i.e. how fast this has become popular):
• Top Ask.com searches: most searched at Ask.com past week;
• Aol.com hot searches;
• Daily MSN A-list;

What’s HOT around social media? 社会化媒体类：

• Delicious hot tags;
• StumbleUpon popular tags (recently popular and all the time);
• Popular Flickr tags (in the last 24 hours, over last week and overall);
• Twitter hot topics: Twitscoop - lists most popular terms discussed at Twitter and displays the trend history in the form of a graph:

What’s HOT in blogosphere? 博客圈：

• Technorati Popular: top searches and top blogs (in the last 48 hours);
• BlogPulse key phrases allow for “trend this” option that graphically represents the trend history:

What’s HOT in eCommerce? 电子商务：

• Amazon tag cloud = which tags Amazon customers use to classify products;
• EBay pulse = popular eBay searches.

What’s HOT everywhere? 综合：

• SEOmoz popular searches aggregate data from most sources mentioned above (Google trends, Yahoo buzz, Technorati, etc).