Cambridge University Press have just released a new series of reprints of out of copyright material in their series Cambridge Library Collection. It includes a range of volumes, with many by Petrie, and is most definitely worth a look.
http://www.cambridge.org/gb/academic/subjects/archaeology/egyptology/series/cambridge-library-collection-egyptology/?options
http://www.cambridge.org/gb/academic/subjects/archaeology/egyptology/series/cambridge-library-collection-egyptology/?options