We are using <a href="http://insight.ly" rel="nofollow">http://insight.ly</a> - It gets the job done and integrates well with Google Apps. There are a few things lacking like an API and the reporting is pretty weak.<p>We are transitioning away to Zoho CRM. So far, Zoho CRM has been great but, can get costly if you have too many users.
My product integrates a CRM, so we dogfood. Works well enough, but sometimes you wonder if it blinds you to anything you're missing.<p>Everyone seems to like it much better than what we used to use, though.