I am using Mixpanel in a Saas App, it's the most advanced analytics platform ever. I have used similar products in the past and Mixpanel beats every other product out there.

The main feature I like is the funnels, which give some actionable insights regarding my product, I was able to make feature decisions based on this. I was even able to make critical decisions regarding the work flow.

Also now with their People feature , I am able to automate email notification based on users activity.

We use Rackspace Cloud Files to host static assets ( js/ css / some media ) and we're really liking it.

tbh we use it because of the ability to serve files from Akamai CDN. You get the worlds best CDN server for a fraction of the cost.

To conclude, it might not be as cheap as S3 , but if you care about files being served at the fastest way possible then Rackspace Cloud Files is the way to go.

We use Unbounce to create landing pages for marketing campaigns. Best part about Unbounce is that we can create highly tested landing pages in a matter of minutes.

Their template repository is very good and they have templates for every sort of industry.

If you are a startup without a dedicated designer or front end guys, this is the best tool to create landing pages without spending much money.