Does anyone know of any discussion of the the "sefer Milkhamot Hashem" mentioned in Bamidbar 21:14? Someone had asked me about the content of the book and I had no idea of what to answer him.
(To see the commentaries in Hebrew, click on the link in Dan's comment.)
The explanations of "The book of the wars of G-d" (ordered by subject):
Rashi and Sforno and Rashbam: The oral traditions/tellings of miracles
Shadal: Songs people sing about G-d
Ibn Ezra: An actual book dating from the time of Avraham that is no longer extant
Ramban and Daas Zekeinim: An actual book, because in every generation there's someone who records things that happened
Targum Onkelos: An actual book that records the encounters G-d had at Yam Suf, etc.
Targum Yonasan and Yerushalmi: The Torah, which records G-d's wars
Midrash Agadah: The book of Shemos
Ohr HaChaim: G-d's "record book" of which countries own which land
Netziv: The book about the conquer of Eretz Yisrael, which started when they defeated Sichon
Rabbi Yehoshua Inbal in his essay in Hebrew "שחזור קטע מספר הישר" (The Restoration of a Segment from Sefer Hayashar) gives an overview of several different opinions on what Sefer Hayashar (another lost book) was. Then, following in the footsteps of commentators such as Rabbi Avraham ben HaGr"a and the Ibn Ezra, puts forward his hypothesis that Sefer Hayashar includes within it Sefer Milchamot Hashem and the meshalim mentioned in Bamidbar 21:27-30, together with other, more ancient poems about the might of Hashem passed down through the generations, and then suggests that as this book was still in the hands of the prophets, parts of it can be traced throughout Tanach and attempts to restore a section by putting all of those bits together.