With you on Sibelious, thats a lovely piece. You can add Finlandia by the same composer.
Beethoven's 7th, 8th and indeed, the 9th are all awsome symphonies especially when you consider that he was almost totally deaf by the time he wrote the last one.
Beethoven's 6th (Pastoral)
Fantasia on a Theme by Thomas Tallis by Ralph Vaughan-Williams (Britain's Greatest who funnily enough also did a luscious Pastoral Symphony)
Five Variants of Dives and Lazarus by Ralph Vaughan-Williams
The Lark Ascending by Ralph Vaughan-Williams (imagine yourself soaring over the South Downs to this one)
Finlandia by Sibelius
Cello concerto no. 1 by Charles-Camille Saint-Saëns
Organ concerto by Charles-Camille Saint-Saëns
Cello concerto by Sir Edward Elgar
Violin concerto by Sir Edward Elgar
Fantasia para un gentilhombre by Joaquin Rodrigo
Concierto de Aranjuez by Joaquin Rodrigo
Tons of Mozart especially his Mass
Most of Frederic Chopin's mesmeric piano work especially Etude Opus 10 number 3
Seconding the Vaughan Williams "Lark Ascending" and "Dives and Lazarus".
Mahler's Second (Resurrection) Symphony. I saw Abbado and the Boston Symphony do this in '79, and when they finished the piece nothing happened -- for ten full seconds. Then the place went absolutely ape-shit -- like a Celtics playoff game. Never heard a classical audience act that way before or since.