See Mashable for 50 tools to help track traffic. You might want to check out
- Google Analytics, for the price (free) you can't beat it. It does require persistent cookies, so is not right for dotgov without a waiver.
- StatCounter for smaller sites, includes a nice set of reports for general website reporting.
- Sitevolume you can track keyword volume on popular social media sites. You can see which words and phrases resonate and compare terms.