Apple releases daily sales reports in iTunes Connect, which you can view online or download. These reports are lists of data - the name of the app, how many sold in which country, what your profit was. You can import these into any spreadsheet program, like Excel or Numbers).
AppViz is a Mac app that makes it easy to track your sales. It can import the reports from the web or from a downloaded file, and display charts of your daily, weekly, and monthly sales.
AppSales is an iPhone app, but it's not available on the app store; instead you download the source code and install it yourself on your iPhone. (You can only use this if you're an iPhone developer; you'll need your developer certificate to install it on your device. You can also build it as an ad hoc distribution to share it with your dev team.) Free and open source.
AppFigures is a web-based solution for tracking app sales.
Usage / Analytics
Want to know who's using your app? There are several analytics options for iPhone apps. (You'll have to compile the necessary code into your app in order to utilize analytics services like these.)