Dave--when I was in school we used the Walter Piston book on harmony. It's pretty dense and deals primarily with baroque/classical as opposed to the later romantic era stuff. Unfortunately I no longer have my copy but they have it on amazon. And check out your local library, too.

http://www.amazon.com/Harmony-Fifth-Walter-Piston/dp/0393954803/ref=pd_bbs_sr_1/103-6518360-8826233?ie=UTF8&s=books&qid=1175867196&sr=8-1