Ugh, the Messiah is dull, I really tried to get into it! I like Handel's coronation anthems and Music for the Royal Fireworks.
There's a BBC Orchestra rendition of the Fireworks music on Youtube that is currently my favourite piece of music in any genre. I'm something of an ignoramus when it comes to all forms of music, but Handel seems to have composed so many of my favourites - the Fireworks, Zadok the Priest, the Water music, the Sarabande that Kubrick used so effectively in the film Barry Lyndon
Other ones I like are Beethoven's Pastoral Symphony, which is used with very sharp irony in Soylent Green
, Bach's Air on a G String, Pachelbel's Canon, the Moonlight Sonata... yes, all the tracks you'd find on a That's What I Call Classical Music album.