Google Analytics -- free analytics, page tracking with some event tracking, no user-level tracking
Mixpanel -- user action tracking, A/B testing, 20M data points free per month
Heap -- user action tracking, 50k sessions free w/ badge
KISSmetrics -- expensive, starts at $220/mo
Woopra -- user action tracking, 30k actions/mo free
Implement: Google Analytics and (Mixpanel or Heap)
Google Analytics -- free analytics, page tracking with some event tracking, no user-level tracking
Mixpanel -- user action tracking, A/B testing, 20M data points free per month
Heap -- user action tracking, 50k sessions free w/ badge
KISSmetrics -- expensive, starts at $220/mo
Woopra -- user action tracking, 30k actions/mo free
Implement: Google Analytics and (Mixpanel or Heap)