Inspired by Menachem Mendel's post Google’s Jewish Books, I will list some of my own discoveries on Google Books and other useful e-books freely available online in other places which are more difficult to find (I don't consider browsing JNUL or Hebrewbooks.org terribly difficult). I will (probably) only list books that are in English or Hebrew, although there is obviously potential wealth in other languages.
1) Moses Israel Landau's edition of the Aruch (1819-1835): I, II, III, IV
2) Joseph Derenbourg's edition of Saadiah Gaon's Tafsir (1893).
3) Moise Schwab's Talmud Yerushalmi Berakhoth, English translation of the French (1886).
4) Abraham Berliner's edition of Rashi (1905).
5) Leone da Modena's autobiographical Ḥaye Yehudah.
6) Yasha"r Reggio's edition of the aforementioned Leone da Modena's Behinat ha-qabbalah, with Qol Sakhal and Sha'agat Aryeh.
7) Nachman Krochmal's More nevukhe ha-zeman.
8) Hayyim Yoseph David Azulay's Shem ha-gedolim he-ḥadash.
9) Samuel David Luzzatto's Isaiah with Italian translation and comentary, 1867.
10) Yom Tov Zunz's Namen der Juden (see, I've already violated my Hebrew/ English quasi-rule).
11) Adolph Jellinek's edition of the Haqdamah to Minchat Shai
12) Ḥayyim Heller's Al Targum ha-Yerushalmi la-Torah (1921).
13) Simcha Pinsker's Likute Kadmoniyot.
Much more to come, I think.
Also, please note that the time is short for me right now. I will edit this post with more information about the names and works in this post.