Guys - do any of you read books? There are loads of publications out there which give full listings of all the civil aircraft national prefix letters. One that instantly springs to mind is the Ian Allan publication "Civil Aircraft Markings". Any of the airline fleet listings books such as "JP World Airline Fleets" would also contain these details.I'm sure this info is easily obtainable on the Internet too.
I "discovered" the national identity letters when I was about 9 or 10 years old. My dad bought me the 1966/67 "Observers Book of Civil Aircraft" as a Christmas present and all the reg' prefixes were listed at the front. The 'net is fantastic but you can't beat books for good basic data. I've been able to answer some questions on historic queries posted on this forum over the last few days merely by pulling down the relevant book off the shelf. Admittedly my library has grown somewhat over the intervening 34 years since I bought my original "Observer" book (which I still have, by the way - and which I still find useful, even now).
Also, your local library sjould be able to provide you with plenty of book material (and magazines too) for free. Here in the UK libraries are an invaluable source of information, sadly underutilised.