Translation with very useful appendices:
**R. Liuzza, Beowulf Ontario: Broadview Press, 1999.

Absolutely essential
R.E Bjork and J.D Niles, (eds.) A Beowulf Handbook (Exeter, 1996) - a collection of short essays surveying the history of various aspects of Beowulf scholarship (metre, history, gender roles, sources and so on) followed by chronological bibliographies. This is a very valuable tool for further reading on the poem.
Roberta Frank, 'Germanic Legend in Old English Literature' in M. Godden and M. Lapidge, edd. The Cambridge Companion to Old English Literature(1991)

Analogues
G.N.Garmonsway, and J.Simpson, Beowulf and its Analogues (London 1968) - an invaluable collection of translations of many texts related to Beowulf
D. Calder, R. Bjork et al. Sources and Analogues of Old English Poetry, vols. 1 and 2, (1976).
plus material in Liuzza.

 Norse material
Saxo Grammaticus, History of the Danes, the first nine books, trans. Peter Fisher and ed. Hilda Ellis Davidson (Woodbridge, 1979)
The saga of the Volsungs, trans. Jesse Byock (Enfield, 1993)
**The saga of Hrolf Kraki, trans. Jesse Byock (Harmondsworth, 1998)

if further interested in Norse myth:
The Poetic Edda, trans. Carolyne Larrington (Oxford, 1996) - with Snorri's Edda (below), the basic source for Old Norse mythology
Snorri Sturluson's Edda, trans. Anthony Faulkes (London, 1987)

Tacitus, The Agricola and the Germania, trans. H. Mattingly, rev. S.A. Handford (Harmondsworth, 1970)

History and Germanic Background

E.O.G. Turville-Petre: Myth and Religion of the North, (1965)
 N. Eliason: 'Healfdene's Daughter', in Nicholson and Frese, 3-14.
N. Eliason: 'The Burning of Heorot', Speculum 55, (1980), 73-83.
F.C. Robinson: "History, Religion, Culture' in Bessinger/Yeager, (1984)
**C. Clover: 'The Germanic Context of the Unferth Episode', Speculum 55, (1980), 444-68.