List of sites to use to find out what people are searching for on the web:

• AOL Hot Searches: Top current queries, or see those in the last hour, last day and within particular categories.
   
• Ask IQ: See top searches at Ask.
   
• Dogpile SearchSpy: Choose to see either a filtered or non-filtered sample of top, real-time search terms from this popular meta search service. Sister site MetaCrawler offers a similar MetaCrawler MetaSpy service.
   
• Google Trends: Allows you to tap into Google's database of searches, to determine what's popular. View the volume of queries over time, by city, regions, languages and so on. Compare multiple terms, as well. See our review: Google Trends: Peer Into Google's Database Of Searches.
   
• Google Zeitgeist:What people are searching for at Google and its associated specialty services in a variety of categories. There are versions for various countries, as well.
   
• Lycos 50: Long-standing service showing top searches at Lycos each week.
   
• MSN Search Insider: Top 200 queries on MSN Search (annoyingly in random order), top "movers" in TV, sports and music, and a "duels" feature pitting top queries in a race against each other.
   
• Yahoo Buzz Index:Shows you what's hot and what's not in terms of search topics at Yahoo.

Also see:

• dWoz Search Phrase Lists: Great directory of services like those above, for search engines large and small, across the web. Also see the Search Spies & Voyuers category.
   
• Google AdWords Keyword Tool: Enter a term or terms, the use the drop-down box to see the popularity of terms and popularity over time.
   
• Yahoo Keyword Selector Tool: Formerly called the Overture Keyword Selector Tool and the Overture Search Term Suggestion Tool before that, this free service is primarily designed to help advertisers who wish to select terms to target with ads on the Yahoo network. But you can use it to see how popular particular terms are.
   
• Researching Keywords: For Search Engine Watch members, this provides an annotated rundown on key tools useful for search marketers needing to perform search research for their campaigns.
   
• Search Term Research and Search Behavior: These categories of Search Engine Watch's Search Topics area compile articles on the subject of how people search from across the web and stretching back to 1997. Available only to Search Engine Watch members.