Depending on the data, you can either use one of the following.
Google Spreeshet / Charts: I use this for real time analytics generated from our system to quickly visualize the information. There's a simple JSON API that lets you pull that in although their is limits on the amount of rows you can use.
Geckoboard: They provide dashboard type widgets you can configure to show you real time trends and information.
Highcharts.com: Simple chart generator. We use this in our Admin Dashboard to visualize all our data include cohorts and weekly KPI's.
I like simple and free.
What kind of visualization do you need to do? For basic graphs, such as traffic growth, year on year growth, and more I use Excel. It depends on who you're reporting to, but you can usually define down the variables that matter to the company and visualize them on one dashboard.
If all of your data is within Google Analytics, you can build a full dashboard within Analytics to show your top-line metrics, but this usually doesn't provide the granularity of data that you need to see.
Finally, there are multiple tools for data vis depending on your need. Gephi for visualizing large sets of data, multiple tools like visual.ly for making infographics, and of course a myriad of freelancers out there to visualize your data for you if you need to make it actionable and presentable.
Hope this helps. Feel free to contact me if you need more info!
I see two important players missing in the answers already provided so I wanted to add them here.
If you are planing to embed charts in your website and are fairly comfortable with programming, consider d3.js which is a very versatile visualization tool.
If you need to analyze data and create interactive dashboard to visualize the data that you have using minimum programming, consider Tableau which has both server and desktop editions.