Hebrewbooks.org has updated their site to include many more seforim. Here are some of the many interesting seforim available:
1 - Maamer HaTigalachas - Y. S. Reggio - See here for an excellent description of this sefer.
2- Tocho Ratzuf Ahavah - M. S. Gerondi - I don't know anything about this particular book but based on the authors reputation (see M. Hershkowitz's article in HaDarom) it should be worth looking into.
3-Igrot R' Yitzchok Isaac Halevi (Note: All volumes of Dorot HaRishonim are also available there) - This is based on A. Recihel's doctoral dissertation and has been out of print for years. It includes in extensive biography and letters. It is generally believed that Halevi's harsh polemics against the Maskilim was because he was angry at their role in the closing of Volozhin (although it is hard to see a connection between Graetz and the Russian Maskilim who were very different in style). My own impression from the letters is that Halevy had a far too high opinion of his own abilities as in historian and a far too low opinion of anyone elses (see the comments in the letters on R' Dovid Tzvi Hoffmann who was unquestionably far greater then him). In point of fact, little remain of Halevy's theories - S. Albeck (and later Halivni) destroyed his theory regarding the redaction of the Talmud (Sinai), R. YY Weinberg - his theory of Yesod Mishna (Seridei Esih 4), L. Ginzberg - his theories regarding the Geonim (Geonica - English part). Note also that when referring to the German Rabbis he refers to them by their last name whereas the Lithuanian Rabbis are referred to with their proper titles. His Sefer on Sefeikos - Batim Levadim has been published a few years ago.