I read last night that Twitter released their analytics to everyone on the platform. Really smart move by them and the analytics look pretty sweet. I have to imagine they will have a freemium version of analytics in the coming months but that is purely speculation.
I took a screenshot of what my follower chart looks like. While this data is readily available thru other services, it looks pretty sweet thru Twitter and was impressed with their execution.
The way you access this is thru the Twitter Ads function which is located under the Settings drop down. Once under Settings (the little widget/gear), go to Twitter Ads then to Analytics.