RJMetrics allows you to get your reporting dashboards set up, and helps you focus on your key metrics. It only costs $500/month. You basically send them your entire database and they can run all sorts of queries against it.
We used Mixpanel a lot, particularly in the beginning, but they get really expensive as you get bigger. So now we use Google Analytics and RJMetrics--that's what we'd recommend for larger companies ... Before you start with Mixpanel, try to use Google Analytics because they have most of the same features for free, and Mixpanel, though it’s good for a lot of things, can get pretty egregious in pricing. We don’t have such a big audience--we use it mostly for conversion funnels, and it's over $1,000 per month.
We thought we’d grown out of Customer.io, but we've been frustrated with every other provider, so we stuck with them. They're good for companies of all sizes, and I'd recommend them to anyone.
It seems like SurePayroll has been in the business for a long time. There are a lot of nuances in the payroll space, so we wanted to go with an older, more established company, as opposed to some of the new startups in this space.
Our engineers use Basecamp and they love it.
We also used Pivotal Tracker, but we switched to Trello, which we're very happy with. Trello was just easier to extend to our organization outside of product, including marketing, etc., and Pivotal Tracker had been used only by our contractors.