How to reduce the log file size without shrinking it in SQL server
Once the log claims disk space the only way to get it back is to shrink.  Checkpoints and truncation will free up space within the log file (now available for future use by the log) but the actual footprint of the file on disk stays the same.

Read these articles for good information not only about how this works but the pro's and con's of messing with it.  Most DBA's would agree that shrinking is not a good idea in most normal cases (as you eluded to in your question).

http://msdn.microsoft.com/en-us/library/ms365418.aspx

pros and cons

http://social.msdn.microsoft.com/Forums/en/sqldatabaseengine/thread/a9e92f1b-7a27-4999-b241-eadadbb0a057