Storable/DB_Files are not only obvious - they're a good solution! However, you might want to try using MLDBM::Sync, which will take care of locking issues for you. You could also use one of the Cache::Cache modules. The one that uses a tree of files for storage is especially good for applications with many simultaneous users since it does separate locks for each entry. (Row-level locking!)

If this were a big commercial site, you would naturally want to use a RDBMS for reliability and scaling, but these simpler methods are easier and faster for a personal project site.