music recommendations

Most traditional classical music doesn't do it for me. However I love Ralph Vaughan Williams and Arvo Part and have extensive collections of both. What other artists do you think might appeal to me?
Danny Elfman/Serenada Schizophrana.
Univers Zero/The Hard Quest.
If you like RVW, you might also like Gerald Finzi.
I love Vaughan Williams as well as traditional classical music. I would suggest you try Sibelius and Delius if you haven't yet.
If you like Vaughan Williams, you might also explore

Malcolm Arnold (e.g., Beckus the Dandipratt, Eight English Dances, Four Scottish Dances, Symphony No. 2)

Frank Bridge (e.g., Cherry Ripe, Sally in our Alley, Sir Roger de Coverley, Suite for String Orchestra)

George Butterworth (e.g., A Shropshire Lad, The Banks of Green Willow)

Hubert Parry (e.g., Lady Radnor's Suite)
Depending on what it is about Arvo Part's music you like, you might like:

Andrzej Panufnik (e.g., Sinfonia Mistica, Sinfonia Sacra, Landscape)

Eduard Tubin (e.g., Symphony No. 4, Estonian Dance Suite)
Alan Hovhaness. You might also like early music: a capella vocals performed by The Tallis Scholars, The Clerks' Group, the Paul van Nevel ensemble, Cantus Colln, The Sixteen, and others.
Rushton has given you some good composers to ponder. Along those lines you might also like Edward Elgar, particularly his less well known works like Starlight Express. He directly precedes RVW in British musical history. Also try William Walton, particularly his Cello Concerto. Walton is a musical decendent of RVW and gives you a glimpse of British music just following RVW.