One of the more frustrating aspects of Batman: Arkham Asylum, for me, was the lack of a minimap in the hud. I appreciated the clean view afforded by a minimalist HUD, but it made hunting up Riddler Trophies and clues, with the aid of a GameFAQ, of course, a chore marked by constant pausing.
While it's not a minimap, an official map application for iOS devices, available now, should make the process more convenient in Arkham City. It's more or less a strategy guide for completionists, showing the location of more than 350 collectibles, broken down by character (Batman, Catwoman) and including locations of Riddler riddles.
It spares you from turning pages and marking items off of them, as the app allows the user to mark which ones he's found on the screen. So stumbling across one on another mission and reminding yourself to come back to it, or just going through the collectibles in order as a side job, is no longer the most painless way to finish the task.
The app is $2.99 and it is official. It has a few seconds of loading time in and out of each map, but they are zoomable.