There is a built in statistics package (the "Statistics" tab in Edit Mode) that would probably have the data you need.
Here's an old article about it: Did you know that there is a built-in statistics function in Edit mode?
I took a look through the API, but there doesn't seem to be anything to grab the stats in aggregate. You get the stats for a single page, but I don't see anything to grab them all at once (admittedly, I didn't look very far).
(I thought perhaps you could drop straight to the database, but after 30 minutes of curiosity, I've determined it isn't easy. Statistics are logged through log4net into -- as near I can tell -- the SqlObjectStore. I got a little lost at that point, but suffice it to say that it's not just a simple, flat table.)
I'd recommend using an external system like Google Analytics, the built-in statistics is something we are phasing out for something better.
Have a look at this for inspiration on Google Analytics API:
I am currently creating a module that lists the most read pages on my EPiServer 6 site for a certain time scale i.e. the last month or week etc.
I am planning on using Google Analytics and filtering the results from there. Does anyone have any other suggestionsfor technologies I could use (hopefully something inbuilt within EPiServer which I am yet to use)