Skimmed through the whole thread so that I don't post a duplicate. A few of the good ones have already been posted such as Debussy.
I like Nicolo Paganini's work
Caprice No.5
And the fan favourite, Caprice. No.24
.
There are other Caprices for solo strings. No. 6 is good too.
Aside from the classics, I like orchestral arrangements in general. I still believe Silverchair's Tuna in the Brine arrangements is one of the most satsifying modern orchestral arrangements to date. I rate Tuna in the Brine close to Bohemian Rhapsody in terms of arrangement complexity, though maybe I have this opinion because I'm not that big a fan of Queen (I'm a Led Zep fan).
Tuna In the Brine with the band included. Silverchair, for most grossly underrated and should be inducted in the Rock N Roll Hall of Fame.