Mixpanel is awesome. I love it to death. I was an early adopter so I have just a TON of data points with them. Unless we explode in popularity, it isn't all that expensive.
Crashlytics is great for finding technical issues in your app, because you can see exactly where your users are experiencing crashes.
Even though we have a small team, we use Slack for our app beta testers. We recently moved to the paid plan. But their free plan was still awesome. You can upload custom emojis which is probably my favorite feature. Slack is surprisingly entertaining, even though it's really functional. It adds whimsy to daily work.
I feel like I overpay for what I'm getting with UserVoice. We really don't get all that much email traffic to begin with, so I usually respond to them all myself. It would be great if you have a million people emailing all the time, but it's a bit extraneous for our company. I don’t really take advantage of UserVoice’s other features.
QuickBooks is OK, but we can't use the online version, unfortunately. We have to use the native application because the online version doesn't handle alternate types of currency. A few of our customers and vendors use Euros.
GitHub is key to everything we do. Given that we’re always working on multiple development projects, GitHub is especially important for us. Their product is awesome. We can use it for issue tracking too. Any project development that we do is connected to GitHub in some way.