Sorry, I missed your message CWMV! I didn't use any books in particular as the ones I have at home are really secondary resources. I did have an excellent magazine series which tracked the 109s development in a flow chart. It was full of minor errors (mostly relating to loadouts) but using info from the 109 lair, Luftwaffe Experten Message Board and from community members, I was able to cross reference with it and overcome the minor errors. After that, it provided a pretty clear illustration of the 109 progression.
Now I can't remember the exact book off the top of my head (currently away from home) but there is a bible on the 109 that almost every other book on the aircraft has referenced. I wouldn't be surprised if it is the book by Caidin that Andytothed has recommended.
Glad you like the new version. In the coming month, we will be packing this into SFS with a few other added goodies (e.g. combining with early 109s)! And indeed, I'm not a huge fan of the B-2, it is incredibly underpowered, but being such a handful to fly, I'm actually really enjoying!