JFile Pro - The first full featured database program for the PalmPilot. Supports up to 30 databases with 50 fields each, many field types, multiple sorting and filtering options. - http://www.land-j.com/jfile.html
List - Database program for the PalmPilot. Supports up to 12 databases, 3 fields per database, simple sorting. Freeware. Source available. - http://www.magma.ca/~roo/list/list.html
Palm OS Database Comparison Review - Excellent review of the available database software for the PalmPilot. - http://www.the-gadgeteer.com/databases-review.html