Antipas Christadelphians: Handel's Messiah Midi Page: Complete libretto, commentary, nearly complete MIDI.
George Frideric Handel - Messiah: Libretto; WAV files of several movements (at Classical Music Pages)
Handel's Messiah: Complete libretto, with sources.
Handel's Messiah Through the Centuries: Paper by Patrick Findlay: related musical and cultural changes.
Inkpot Classical Music Reviews: Handel Messiah: Introduction; recommended recordings, some with very detailed reviews.
Karpeles Manuscript Library - Handel's Messiah in Beethoven's hand: [scans of two pages of a historically interesting manuscript]
Messiah by George Frideric Handel: Digital facsimile of complete score (1912 Schirmer ed.)
The Messiah Project: MIDI encoding of the "Messiah".