Google Trends allows you to see some of the most popular keyword searches and see their popularity over time. It also allows you to compare the popularity of keywords as well.
You can get started at http://google.com/trends. On the main page, you’ll “hot topics”:
And then more specifically, you can see the “Hot Searches”:
At the top of the page, you can enter your own keywords and compare them if you wish. Just separate each keyword by a comma:
By default, Google Trends shows you the data over the past few years:
As we can see in the above example, Santa Claus is the most popular with a spike at the end of the year. The Easter Bunny is next most popular with a smaller spike in the springtime. The Tooth Fairy is searched the less with only a few very small spikes in traffic in 2010.
In the top right corner, you can change the time period shown in the data. Your options include:
You can also view popularity of phrases by region or specify your search to a particular region.