The Loom of Language by Frederick Bodmer
It goes into comparasins between languages and language families, with lots of examples. I read it first in high school, about 10 times (yes, dorkus erectus here); loved it.
From one of the Amazon.co.uk reviews:
It aims to give the reader the key to learning all Romance languages as a one-er, using their similarities and differences as a useful tool for learning rather than a hinderence. It does the same with Teutonic languages, and how they all do the same, in their own way. From this 669pp book, one can easily learn the core matter of French, Spanish, Italian, Portuguese (on the Romance side of things) and German, Dutch, Danish, and Swedish (on the Teutonic). However, it also gives excellent insights into languages as varied as Latin, Greek, Gothic, Anglo-Saxon, Icelandic, Esperanto, etc. It covers the web of vocabulary, the web of grammar, and all that holds the dynamic world of languages together.
http://www.amazon.com/Loom-Language-Frederick-Bodmer/dp/0850363500/ref=pd_bbs_sr_1/104-9208714-7655914?ie=UTF8&s=books&qid=1173444727&sr=8-1