Google offers a number of tools to help examine search trends over different time periods. In addition to Zeitgeist, which looks at an entire year, Google also offers Google Trends and Hot Trends.
Here's more about Zeitgeist from the site:
Pulling together interesting search trends and patterns requires both computing power and human power too. Search statistics are automatically generated based on the billions of searches conducted on Google. With some help from humans, and a pigeon or two when they have time, these statistics and trends make their way from the depths of Google's hard drives to become the Google Zeitgeist findings. We should note that in compiling these Zeitgeist lists, no individual searcher's information is available or accessible to us. What you see here is a cumulative snapshot of interesting queries people are asking – over time, within country domains, and some on Google.com – that perhaps reveal a bit of the human condition. We appreciate the contribution everyone who searches on Google makes to these fascinating bits of information.
