Symphony: On Mondays, Wednesdays and Fridays, Rachmaninov's #2 in E minor; on Tuesdays, Thursdays, and Saturdays, Berlioz's Romeo et Juliet. On Sundays, Berlioz's Symphonie fantastique. (See what I mean about cheating?)
* Tone Poem, or other non-symphony long-form orchestral work: Scheherazade, by Rimsky-Korsakov. A couple of hours perusing this score will teach one more about the orchestra and the sounds within it than a hundred books on orchestration. (Also Strauss's Eine Alpensinfonie, which I just adore despite the fact that Strauss just wallows in his musical ideas in this work. Seriously, if subtlety is a thing you value, avoid this work like the plague. If I were to name the three least subtle works in the entire classical music repertoire, this one would probably make the cut, along with Tchaikovsky's Piano Concerto #1.)
Piano concerto: Beethoven's Fifth ("Emperor"). (All four of Rachmaninov's, a bunch of Mozart's, and Gershwin's are all runners-up.)
Violin concerto: Mendelssohn's. The first movement has this amazing spot where the soloist holds a low note -- a G, if memory serves -- while the woodwinds sound the movement's second subject high above. Just magical. (And while it's not a concerto, The Lark Ascending for violin and chamber orchestra by Ralph Vaughan Williams is as gorgeous a work as I know.)
Concerto for any wind instrument (flute, clarinet, oboe, horn, etc): Arutunian's Concerto for Trumpet and Orchestra.
Concerto for two or more soloists: Mozart's Sinfonia Concertante for violin, viola and orchestra. (Not technically a "concerto", I guess, since Mozart didn't call it one. But I'm counting it.)
* Work or Musical Passage featuring each of the following instruments:
Flute: Ravel's Bolero. I hate this friggin' piece, but the only part of it that I like is the very first iteration of that damn melody when the flute plays it.
Oboe and English Horn: The wondrous opening and closing bars of the third movement of Berlioz's Symphonie fantastique, when the English horn and offstage oboe exchange a melody that suggests the horn calls of mountain shepherds.
Clarinet: As a former brass player, I have an almost genetic need to make fun of the clarinet. However, it's actually a wonderful instrument that is featured in a gorgeous long solo passage at the beginning of the third movement of Rachmaninov's Second Symphony.
Bassoon: In the last movement of Beethoven's Ninth, the bassoon has a nice countermelody during the second iteration of the famous "Ode to Joy" theme.
Saxophone: Rachmaninov's Symphonic Dances has a good sax part.
Horn: The "On the Summit" passage in Strauss's Eine Alpensinfonie has the entire horn section just pealing out over the combined might of the strings. Unsubtle, yes, but freaking majestic.
Trumpet: I'll limit myself to just two citations: the solo trumpet part in Scriabin's Poem of Ecstasy, and the closing moments of Brahms's Symphony No. 2.
Trombone: Solo trombone features in the "Tube Mirum" of Mozart's Requiem; the trombones as a whole feature wonderfully in the brass chorale theme in the finale of Brahms's Symphony No. 1.
Tuba: What else? The Dies irae in the finale of Berlioz's Symphonie fantastique.
Violin: The recurring violin solo part in Rimsky-Korsakov's Scheherazade.
Viola: The solo part in Berlioz's Harold in Italy.
Cello: When the cellos start the "swirling" of the Rhine's currents in the prelude of Wagner's Das Rheingold. And really, the entirety of the Prelude to Lohengrin is just masterful string writing.
Double Bass: It's hard to think of really good parts for the double bass, isn't it? I mean, they're so important in every symphonic work ever, but they're so rarely featured directly. It seems like it would be cheating to cite that pedal E-flat at the beginning of Das Rheingold, but that's all I got right now! Oh, and the Dies irae from the Symphonie fantastique.
Timpani: Mahler's symphonies always abound with good stuff for the timpani.
Other Percussion: Nielsen's Symphony No. 5, when the snare drummer is instructed to improvise loudly during the slow movement. Done well, it's an amazing passage.
Overture or other short classical work (less than 12 minutes long): Romanian Rhapsody #1, by Enescu. (Strauss's On the Beautiful Blue Danube may be a cliche now, but it's become so for a reason. Percy Grainger's Lincolnshire Posy is a revelation, as are the two Suites for Wind Band by Holst and the Vaughan Williams English Folk Song Suite.)
* Work for Concert Band or Wind Ensemble: Elegy by Mark Camphouse. Were I to be informed by God that my mission on this planet was to go around and force people to listen to a handful of musical works of my choosing, this would be one of them.
Piano sonata: The Appassionata by Beethoven. (I'm not looking up the work number, opus number, or key!)
Other unaccompanied: There's a Bach Partita for solo violin that I've loved ever since I heard it used in Cosmos. I've got it here somewhere, but I'm not getting up to look up the info just now.
Sonata with accompaniment or other music for only two instruments: Brahm's Second Cello Sonata (I'm hoping to buy a copy of this tomorrow, actually.) And as a former trumpet player, I'm probably supposed to like the Hindemith Trumpet Sonata, but I just don't.
Quintet (I'm leaving this four areas open because of my general ignorance of chamber music. I'll try to remember to come back and fill them in at a later time.)
Other chamber music: The Pachelbel Canon as performed by the Canadian Brass.
Latin choral work (mass, requiem, Stabat Mater, etc.): Berlioz's Requiem
Choral work in a language other than Latin: Martinu's The Epic of Gilgamesh. (I also remember liking Britten's War Requiem a lot, but I haven't listened to it in a very long time.)
Opera: M, W, F: Wagner's Der Ring des Nibelungen. T, H, Sa: Berlioz's Les Troyens. Su: Mozart's Die Zauberflote.
Classical work composed after 1950: Geirr Tveitt's Hundred Hardanger Folk Tunes
Classical work composed before 1650: Man, I don't know crap about early music.
Movie Score: M, W, F: Shore's Lord of the Rings. T, H, Sa: Any of Williams's Star Wars scores. Su: Korngold's The Sea Hawk.
TV theme: Dammit, I can't pick any kind of favorite here, so I'll just toss out a grab bag. Mark Snow's X-Files and Millennium themes. Magnum, PI. Once and Again and My So-Called Life. I always liked that jaunty "theme" associated with Seinfeld, although it wasn't really a theme, I suppose. The Simpsons. The Rockford Files.
* Song, Rock: "Dreams" by Van Halen
* Song, blues: I have no idea. Blues isn't really my thing.
* Song, country: "Seven Spanish Angels", by Willie Nelson and Ray Charles.
* Song, other: "Caledonia" by Dougie Maclean
Guitar or lute, classical: No idea. Classical guitar isn't my thing, either.
Guitar, rock, blues, country or other: "Comfortably Numb" by Pink Floyd (although not to purists, I guess.) And there's some wonderful guitar work in "Rough Boy" by ZZTop, a terribly underrated ballad from the 1980s.
Goofy novelty song: "Zip-a-dee-doo-dah", from Song of the South and now the unofficial theme song of Disney World.
Bonus: anything you'd like to add that wasn't on the list: I like Tangerine Dream's albums from the 90s, Melrose being chief among them.
Since Lynn provided official tags, I guess I should as well -- so I'll dump this on John, whenever he returns from hiatus.