kenneth frampton's classic book is a good survey on modern architecture.

for an introduction on theory check colin davies' "thinking about architecture".

If your school offers an appropriate course that you like you could just find the syllabus and try to read what is on it, or maybe the syllabus of another school with a position on the topic that you like. I think you might find that a lot of courses won't have you read whole books, but rather excerpts and articles.

Thanks, monterey.  I will check these out.

natematt, excellent idea, didn't even consider that as a possibility. 

Modern architecture since 1900 by William jr Curtis 

You're also going to want to read Programs and Manifestoes on 20th-Century Architecture.  There's a second book, written to supplement Programs entitled Architecture and Design, 1890-1939: an International Anthology of Original Articles.  My architectural history professors didn't require (or even mention) the second book, but some courses do use it.

I would focus mostly on modern architecture; it's most likely to come up in your other course work.  However, you'll need to study periods sequentially so that the progression is clear.

Thanks for the suggestions. Looking at these on Amazon now.  Some of this stuff looks intense from the previews, very densely worded, but I suppose I should get used to this style of writing now :)

Any other arch history book recommendations?