We're huge security proponents here at TiPb, and that typically means recommending 1Password on the Mac and RoboForm on the PC. 1Password's iPhone app has been available for long time already, providing on-device and Mac synced bliss. Now, finally, RoboForm for iPhone [FREE - iTunes link] is here as well.
It's a first release, it's not quite feature complete yet (on device editing is a priority and coming soon), it requires an online account for syncing (a local Wi-Fi option to sync with the PC client would be nice as well), and there are some bugs (no 4 character master passwords -- though you really should be using much, much longer master passwords!) security is so important we wanted to let you know about it right away, or if you already know about it, we wanted you to let us know how it was working for you.