There are a lot of really wonderful Russian composers: Tchaikovsky, Rachmaninov, Mussorgsky, Prokofiev, Rimsky-Korsakov... and there are also many wonderful, more modern American composers such as Eric Whitacre, Aaron Copland, Stephen Bryant, and their ilk.
My recs: "composer - piece/recording (conductor/performer)"
Modest Mussorgsky - Night on Bald Mountain (Gergiev)
Gustav Holst - The Planets & St. Paul's Suite (Handley)
Claude Debussy - Images & Noctures (Dutoit)
Erik Satie - 3 Gymnopédies & Other Piano Works (Rogé)
Igor Stravinsky - The Rite of Spring / The Poem of Ecstasy (Gergiev)
Philip Glass - Glassworks
Steve Reich - Different Trains / Electric Counterpoint
Krzysztof Penderecki - Symphony No. 3, Threnody (Wit)
So many composers to choose from.
for opera I enjoy Rossini.
You may enjoy listening to Schubert, Haydn, Ravel, Stravinsky, and many many others. Just trying to name a few that haven't already been mentioned.
My favorites kinda change from week to week, but one of my overall favorite styles is Spanish impressionistic, so I highly recommend composers like Rodrigo and deFalla. Also, if you ever have a party and want to make things really awkward really fast, break out the Webern and the Schoenberg.
if you don`t like shostakovich, of kabelavsky, than u really have completely taste than from al my close friend hear. and some of the songs by shostakovich are sad, because he got cancer, so if u don`t like sad songs, don`t listen to the songe that he wrote when he had cancer.