We've mentioned Logos for Mac before, but now there is Logos Bible Software for iPhone (iTunes link), a free app providing access to several translations of the Bible and other Bible study books (most of the ones available at http://bible.logos.com). That's pretty good.
If you create a free account at Logos.com, you gain access to even more free resources. That's even better.
The app also lets you set up reading lists, which is an excellent idea. I've read through the Bible twice in the past few years, and used Mobile Safari on my iPhone to keep up with online lists. This app would have been much easier to use.
Many of the free resources are older, but the English Standard Version (ESV) is a good and fairly modern translation. There are also comparison tools available, as well as dictionaries. (UPDATE: Ryan Burns from Logos.com added a complete list in the comments.)
I'm almost hesitant to mention this next feature. Here's the good news: the new Logos version 4 will work with the iPhone app, giving you access over the Internet to books that you have purchased. That's a pretty killer feature.
Here's the bad news: the Mac version of Logos 4 is not finished. (That sound you just heard was an angry mob of Mac users grabbing their pitchforks off the wall and looking for the kerosene to light their torches.) Logos is developed both for Windows and Mac, and the Windows version beat the Mac version out the door.
The developers explain that the underlying "core" works on both Windows and Mac, and that the pre-release version "reads and indexes the exact same resources and data files as the Windows version. It synchronizes with the server and even uploads and downloads notes, settings, and other data. It can automatically update itself over the Internet. It just needs work at the user interface level, and we're doing that as fast as we can."
They go on to explain that the Windows and iPhone versions are both ready, and delaying "wouldn't speed up the Mac product, it would just delay access for the larger group of users." They describe version 4 as "a completely new product." All of which is fairly reasonable, but unlikely to soothe the nerves of some Mac users who will no doubt feel like second-class citizens.
The iPhone app still offers a lot of functionality, even without Logos 4 integration, and it is completely free.
Do you have a favorite iPhone Bible study app? If so, please let us know in the comments. I realize a lot of you are not religious and may not have any use or affinity for this particular app, but it would be appreciated if you'd let others have a chance to discuss this.