In a previous question I caught the names of a few open-source cataloging systems--Evergreen, Millenium, Horizon, Polaris--but my particular needs are a bit unusual. I've volunteered in a small private nonprofit library for two years as a copy cataloger and then an original cataloger, so I've picked up the basic cataloging rules (AACR2, I think) on-the-fly. The library uses Voyager exported to OCLC; there's a lot of complaining about how expensive and restrictive Voyager is.
I'd like to catalog my own private collection of books/media for archival and insurance purposes. I'm the only person who will be using the catalog, so no need for a fancy interface as long as it's functional. The ability to "tag"/free-categorize is crucial, but I'm sure I can repurpose a few of the many subject-related entry fields for my own organizational methods.
What open-source/free cataloging system would you recommend for geeky personal use?