Apple just made a major enhancement to their 'iTunes Connect' service which is where app developers download sales reports, among other things. Before, the service was a utilitarian, mundane web page, with basic sales data, but was weak on charting and analysis. This gap in functionality spawned a variety of service providers who would crunch your sales reports and create elegant graphs including revenue and rankings. I can't share my sales data or any proprietary screens, as it might be covered by Apple's non disclosure rules for developers, but here is a screenshot from Apple's official iTunes Connect documents on their public-facing website.
I had been using AppViz from IdeaSwarm and was quite happy with it. Their offering was a Mac program that cost a onetime fee of between $30 and $50. It automatically downloaded your reports and provided charts and summaries. There was nothing more to pay and updates were frequent. It was a great deal. Other vendors, like AppFigures, charged per app, so if you have a lot of apps, as I do (about 100) you could be paying hundreds of dollars every month. Since many of my apps are free, it just wasn't worth it.
AppViz followed suit recently and now charges per app, making it cost prohibitive for many developers. AppViz is a great app and service, and I've met the developers, who are quite nice. For professional developers with a few profitable apps, it's a nice fit.
For many independent app developers, Apple's free update to iTunes Connect suits the bill. It's accessible anywhere, via the web, and provides most of what developers will need. I also develop for Android, Windows Phone, and Samsung Bada, so for a completely integrated view, I use Distimo, which is a free service that tries to sell app optimization services.
Whatever service you use, more data and more ways to visualize that data can be a great way to boost your downloads.