My home screen is incredibly boring. Because I have a few devices, and I do a lot of testing with them, I also have to restore them fairly often and it's gotten to the point where I just leave everything in its default location because it's a) easier than rearranging and b) I don't have to hunt for stuff I haven't rearranged.
So, my second screen has become where I move my non-default, but still more often used apps. Typically the exact order will vary due to the reasons above, but the apps are fairly consistent.
I'll list out what I use after the break, but we're really more interested in what's on YOUR iPhone home screen and why. If you're willing to share a screenshot, jump on over to our TiPb iPhone Forums, attach it, and share the details!