From the above conversation, it seems OK to plug your own solution, at least when it applies to the subject at hand. Our application HanDBase has been around since 1998 on the Palm OS. We were and still are very popular on Palm OS, Windows Mobile, s60 and even BlackBerry. We won many awards for best database on both Palm and Windows Mobile platforms over those years. Our iPhone version was released in October and has been very popular and so far well reviewed.
HanDBase is fully relational, supports filters, views, sorting, searching, and supports database creation right on the iPhone or iPod touch. We include a desktop connect feature so you can backup/export/transfer your data between your desktop/laptop and your phone. And we offer solutions for syncing and editing on the desktop as well.
I hope you'd check us out and let me know what you think! We're actively working on adding new features like camera support, GPS, and custom forms to our program as well among other things. Hope you'll like the program!
Here's a link:
http://www.ddhsoftware.com/iPhone
Blessings,
Dave Haupert