I was told by a colleague that Linux Squid and Webalyzer might be the cheapest way to go on this. I appreciate all the replies to my question and the names of some software to do this. I really like that device from Network Intelligence, but that looks pretty costly. I'll be checking out Sawmill here shortly. I've used KiwiSyslogger and I'm not sure it will really do what we need or want it to do by itself. But I'll certainly look into that option as well.
Unrelated to my initial question. We are also looking at something to do Content Filtering. Websense is the obvious solution to this, but again looks very pricey. I'm hearing sites 1/2 the size of ours have been about $300,000 for first year implementation costs. I doubt this is a viable solution. Any ideas on low-cost content filtering solutions?