Bold Green = Title of the Tannaitic Work Itself
A web link indicates a searchable (mostly) free online book or website, while italic book titles without a link indicate printed books which are not available online.
Mishna / Mishnah
Tosefta / Tosephta
Jacob Neusner trans., The Tosefta: Translated from the Hebrew (6 vols.), on D. Instone-Brewer, www.RabbinicTraditions.com
This is not free. Membership fee is £9 (about $14) per year or £24 (about $38) for life.
Just vol.1 Zeraim: Google Book
Mekhilta de Rabbi Ishmael
Mekhilta de Rabbi Simeon ben Yohai /
Mekhilta de Rabbi Shimon ben Yohai
Jacob Neusner trans., Sifra: An Analytical Translation , 3 vols.
Jacob Neusner ed., Components of the Rabbinic Documents, vol.1 Sifra, Parts 1-3
Part 1 of 12: Morris Ginsberg trans., Sifra Dibura Denedabah, with Translation and Commentary
Part 11 of 12: Howard L. Apothaker trans., Sifra, Dibbura deSinai: Rhetorical Formulae, Literary Structures, and Legal Traditions
Sifre Numbers / Sifre to Numbers / Sifré to Numbers
Jacob Neusner trans., Sifre to Numbers: An American Translation and Explanation
Jacob Neusner ed. Components of the Rabbinic Documents, Vol. 12 Sifré to Numbers, parts 1–3.
Jacob Neusner, A Theological Commentary to the Midrash: Sifre to Numbers and Sifre to Deuteronomy. It only has excepts.
Sifré Zutta to Numbers / Sifre Zuta to Numbers
Jacob Neusner trans., Sifre Zutta to Numbers
Sifre Zuṭa Devarim / Sifrei Zuta on Deuteronomy
According to Literature of the Sages, Part 2 (2006), p. 105, this is not yet translated into English.
Hebrew text: M. Kahana, ספרי זוטא דברים .
Midrash Tannaim / Mekhilta on Deuteronomy
Gary G. Porton ed., The Traditions of Rabbi Ishmael, Part 2: Exegetical Comments in Tannaitic Collections. This is on Google Books. There are only very few pages for preview.
Solomon Zeitlin, Megillat Taanit as a Source for Jewish Chronology and History in the Hellenistic and Roman Periods
Semahot of R. Hiyya
According to Literature of the Sages, Part 1, p.394, it seems that even the Hebrew text has not been put together into a continuous whole. I failed to find any English translation, online or printed.
The Hebrew text: Michael Higger, Treatise Semahot and treatise Semahot of R. Hiyya and Sefer Hibbut ha-Keber and additions to the seven minor treatises and to treatise Soferim II.
Minor tractates of the Babylonian Talmud which are considered tannaitic:
Avot de Rabbi Nathan version A
Avot de Rabbi Nathan version B
Ebel Rabbati / Semahot
Dov Zlotnick trans., The Tractate "Mourning" (Semahot) : Regulations Relating to Death, Burial and Mourning
Kallah, the one chapter version
David Brodsky, A Bride without a Blessing: A Study in the Redaction and Content of Massekhet Kallah and Its Gemara, Appendix A, p. 422ff. This is Google Book preview. Some pages are not available.
Derech Eretz Rabbah
Derech Eretz Zuta / Zuta Rabbah, chapter 1-3(4)Jewish Virtual Library