Pageonce for iPhone
In the realm of free applications, no "killer productivity app" for the iPhone exists, but PageOnce Personal Assistant is as close as it gets. Rather than providing its own set of services, PageOnce Personal Assistant aggregates your online accounts and feeds them to your iPhone in one handy, streamlined interface. However, those feeds are limited to read-only status. It's still a handy app for seeing your bank balance (no payments or transfers, though); looking at what's coming up on your Netflix queue; reading your MySpace, Digg, and Twitter feeds; seeing how many minutes you've used up on your monthly cellular account; viewing your cable bill; and scanning your Gmail, Yahoo Mail, and other Web-based e-mail inboxes (no sending messages, though).
In addition to the read-only limitations, I noticed a bit of a lag time between signing up for feeds online and having them work on my iPhone. Also, I really hope PageOnce has airtight security (the PageOnce site claims it does), due to the amount of personal information submitted to get the full range of offerings. As our Ed Albro points out, it's much easier to just check your e-mail inbox than to use the limited read-only feed on PageOnce.
Note: This link takes you to the iTunes App Store, where you can download the latest version of the software.