UnDupe for

From Stevens Creek Software:

There are a variety of circumstances where through no fault of your own you'll find that all the entries in your PalmPilot are duplicated, quadruplicated, or worse! We can't tell you exactly how or why it happens, but it happens. Instead of 500 entries in your Address Book, you'll have 1000, or 2000! If you ever try deleting them yourself, one by one, it's a nightmare. That's where UnDupe comes in. Just run the application, tap on the appropriate buttons, and the duplicates are removed! And it takes up only 10K on your PalmPilot!

With UnDupe you can either delete duplicates from the Date Book, Address Book, Memo Pad, and To Do List (or Franklin Task List if you are using Franklin-Covey software) separately, or just tap on the All button and the program will delete duplicates from each of the four major applications. There's also a "Find Only" mode so you can have UnDupe tell you how many duplicates it finds in each database, without actually deleting them. You can do a fast search, which will catch most of the duplicates, or an "Exhaustive" search, which will find them all.