Are there any online resources that detail the collectibles, and they're locations? (Email conversations, dog tags etc etc?)

The strategy guide outlines them. They are usually found on steps, etc and are quite small. Car keys, emails, dogtags and souveniers.

I've found a good guide for the souveniers if anyone is interested...
http://www.youtube.com/watch?v=St0AAOAsldk
Will continue looking for the rest...