Thanks to Wieland Willker on Synoptic-L for the note that William Wrede's classic Das Messiasgeheimnis in den Evangelien; Zugleich ein Beitrag zum Verständnis des Markusevangeliums (1901) is now available online at archive.org:
Das Messiasgeheimnis in den Evangelien
As usual with archive.org, you can download as PDF, read online in flipbook format and so on.
Also available on archive.org are Wrede's Paulus and The Origin of the New Testament. The latter is also now available on Google Books in toto, including for download as a Google ebook, so you can even read it on your phone:
The Origin of the New Testament
For earlier comments on the availability (and non-availability in some places) of the English translation of Paulus, Paul, see comments over on the NT Gateway blog and here on the NT Blog.