Programmer happiness ... duh!
We're a full-stack Rails shop.
Phenomenal tool for API development.
It's Github ... it's awesome.
We use Rackspace for our CDN for all assets.
RDBM and Document storage combined with good performance makes this a must-have for HomeActions.
Not the biggest fan but it's easy to use and integrate into Airbrake.
DO runs our hardware.
We send all emails via Mailgun (and we're an email sending company)