For any general overview of the Middle Ages I always reccommend Warren G Hollister's
Medieval Europe: A Short History. Emminently readable -- and even entertaining at points -- its a great resource. Amazon has it listed for almost $50 for a pb (!!! I bought mine new for less than $30 around 5 years ago), but hunt around at the college used text websites (IIRC
www.follett.com is one) or even at the college bookstore if you live near one. Beyond that I'll second the reccomendation for Ospreys. Although most of mine are from a later period, the medieval Ospreys -- especially the later ones -- are excellent. I would avoid
Normans, Vikings, and Saxons] which is an older title and not so good anymore. Although as one poster mentioned above they are "history lite," I think that's unfair as they really explore topics that are either not in vogue or just not popular amongst professional historians. I personally found
In Search of the Dark Ages interesting but again history lite; a more focused or professional book covers the same ground and more. Last but not least I would pick up a copy of
History of the Franks which covers part of this period, and is very illuminating on post Roman politics, Germanic culture, and the relationship between the new German kingdoms and the old Roman civilization.
BTW, if you have other questions, drop me a line. I have a history degree, and although I concentrated in a later period (the 12th C Rennaisance and the Late MA), I might be able to help or dig around for more resources.
Damon.