How do I get an new email notification icon on the status bar of an iPod Touch?
This is not built-in to iOS, but there are jailbreak tweaks like Notifier, OpenNotifier, et al. If you've jailbroken your device, try searching Cydia.

Once iOS 5 launches, it'll include notification center which consolidates notifications in an overlay that can be accessed by swiping down from the status bar, similar to Android, but still different from what you're asking about.