Mixpanel is by far our favorite. We use it for all of our clients' analytics tracking, and it’s very developer-friendly. Mixpanel’s pricing is high, but I believe in paying for quality products when it comes to developer tools.
Google Drive is OK. It’s not my favorite service but gets the job done. I don't like the UI for searching docs, but Google continuously makes improvements and the service is becoming easier to use.
Justworks makes it easy to track employees (W2) vs. contractors (1099), and make payments. The itemized breakdown of taxes required for payments is useful. It's also a clean and uncluttered platform.