I high recommend Gifford's.  The people are friendly, it has a great selection of flowers and the prices are great.  I just moved here from Chicago and enjoy walking by the shop on Broadway everyday and seeing all the flowers.  I have ordered off their web site several times and have been thrilled by the flowers and service. Portland is a great city and Gifford's is definately a plus.
Pros:  Convient, selection, service
Cons:  Can be very busy and crowded at times
                        
more