Cable, Thomas. The English Alliterative Tradition. Philadelphia: U of Pennsylvania P, 1991.
Creed, Robert. Reconstructing the Rhythm of Beowulf. Columbia: U of Missouri P, c1990. Another from the oral-formulaic side. Not read; reputed to be poor.
Fulk, R.D. A History of Old English Meter. Philadelphia: U of Pennsylvania P, 1992. Learned; requires stamina.
Hoover, David L. A New Theory of Old English Meter. New York: Peter Lang, 1985. Read with caution.
Kendall, Calvin B. The Metrical Grammar of 'Beowulf'. Cambridge Studies in Anglo-Saxon England, 5. Cambridge: Cambridge UP, 1991.
Pope, John Collins. The Rhythm of Beowulf. 2nd ed. New Haven: Yale UP, 1966. A classic.
* Russom, Geoffrey. Old English Meter and Linguistic Theory. Cambridge: Cambridge UP, 1987. For the linguistically minded, a fine explanation of Old English meter.
Sievers, Eduard. Altgermanische Metrik. Halle: Max Niemeyer, 1893. The guy who figured it all out. If you know German, have a look.
Whitman, F. H. A Comparative Study of Old English Metre. Toronto: University of Toronto Press, 1993. Not seen.