I've been happy with Mixpanel for event-driven analytics. Straightforward API and good customer service.

And the real killer feature for me is you can get a dump of every event you've ever logged with all their properties. Which means I can do complex analysis on the raw data and it also means I can take my data with me if I ever decide to leave.

I also evaluated keen.io which was very nice, but is geared more towards developers.