Smaller pieces - Britten's Rejoice in the Lamb is a gorgeous sing, as is his Hymn to St Cecilia (unaccompanied - I love anything unaccompanied, including madrigals).
There is just so much crammed into Hymn to St Cecilia! It's particularly satisfying if at the end of 10 minutes you find the pitch hasn't changed at all. A colleague of mine always wants to change "O wear your tribulation like a rose" to "O blow your tribulation like a nose"!
Jaakko Mäntyjärvi's 'El Hambo' is great fun, and allows the performers to clap, stamp and shout as well as singing pseudo-Swedish nonsense. I love many madrigals - one favourite is Morley's 'Fyer, fyer' which is very exciting (especially if one singer gets lost!).