tools for reporting session activity

I'm working on a redesign for a client who wants to add session tracking to their site, either using PHP4's built-in session functions (my choice) or mod_session (theirs). What are the best tools to generate reports of session activity? They love the look of the reports WebTrends generates, but I've never been too satisfied with their product, and am not sure they would provide the kind of detail the client wants. They are interested in things like most popular site entrances and exits, popular paths through the site, entry pages leading to purchases, and total unique users in various virtual domains they are running on the site (it uses named virtual servers to attract different kinds of users to their main site). Of course price is a consideration. Most of the higher-end reporting tools are very expensive, and overkill for their needs. I've used Analog mostly in the past, but it doesn't address user tracking very well. So what do you do with all this great session data you've collected?