I made an entire thread about alternative, you can look at it if you want recommendations for that type of music. Phantom of the Opera has some great songs, my favorite is All I Ask of You. My parents really like ABBA! Me, not so much, but I've grown up listening to 80s music every time we go somewhere. It's kind of grown on me. For piano, look up the backing track for Roses by Luke Christopher- there is a video on youtube with just the piano and it is awesome! Also, I will always suggest listening to Fall Out Boy. Sad songs include-

All of Me by John Legend

Addict With a Pen, Goner, Kitchen Sink, or any other song by Twenty One Pilots (though you might not like their songs, they scream sometimes)

Jet Pack Blues by Fall Out Boy

If You Could See Me Now by The Script

Cancer by My Chemical Romance (or Twenty One Pilots, they did a cover for it)

Trouble by Halsey (I'd reccomend listening to Trouble on 1 mic, 1 take, which will pop up on YouTube if you search that)

Sail by AWOLNATION

Demons by Imagine Dragons

Better Than Yourself by Lukas Graham

Stone Cold by Demi Lovato

Here by Alessia Cara has been one of my favorites for a long time. It is so relatable, especially if you're an introvert! She has a beautiful voice and good messages to her songs- I recommend listening to her. I love love love the singer Sia, but she has a pretty raspy voice so I don't think you'd like her as much. LISTEN TO MELANIE MARTINEZ! SHE'S SO GOOD! Rise Up by Andra Day is a good one, and so is Thinkin Bout You by Frank Ocean, if you like R&B. Some 80s songs I'd recommend-

Piano Man by Billy Joel

Bohemian Rhapsody, Don't Stop Me, We Will Rock You, or anything else by Queen because they are great

Dream On by Aerosmith

Cool Change by Little River Band

Signs, Signs, Everywhere a Sign by Five Man Electrical Band

Sweet Dreams by Eurythmics 

Wow, looking back at this post I realize I have a very odd taste in music. That's about it, I think. 

Hm... how do you feel about Japanese voice synthesizers? Because a lot of Vocaloid songs have beautiful instrumental, and quite a few have what I think are meaningful lyrics.

Here are three completely different beasts, for instance:

Rolling Girl by Wowaka feat. Hatsune Miku 

This is a very well-known song, and for good reason! It's got an instrumental where a fast-paced piano is very prominent, kind of rock I guess instrumentally. Miku is supposed to ba a sixteen-year-old girl, she has a high-pitched voice that's a bit generic but (I think) still pretty enjoyable. The lyrics are really vague and up for interpretation, and some of them are very sad. The video I've seen is beautiful. 

Soleil by Travlota-P feat. Kagamine Rin 

This is a lot slower than the other two I've mentioned here, and the instrumental is more... light I guess? It's hard to describe. This is a story song, again up for interpretation, but the idea is less vague. Rin in this song seems to have some power that takes evil from people? Anyway, I won't give away too much.  

The Lost One's Weeping by Neru feat. Kagamine Rin 

This is another fairly popular one, again for good reason. The again fast-paced instrumental is definitely rock this time, with a pERFECTLY GLORIOUS GUITAR, and Rin's voice works with it very well. It's a bit sharper and more, how do I say this, warm? than Miku's. The video is great, and the lyrics are a heartbreaking criticism of the school system.

I'm not great at recommending but here have some songs I like and I think are pretty meaningful!  

tOP TOP

Topsy!

Aaah my spelling/aah auto correct! *I don't KNOW! Not I don't no! sorry!

I have an odder taste-

Blondie: The tide is high, Heart of Glass, Rapture, Atomic, ....

Nirvana: (WARNING!! These have negative messages, but a great beat. Ex. "I'm so happy, I like to take from my friends..")-You know what? I won't reccomened this.

Blitzkreig Bop- By the ramones

Shatter Me- by Lidnsey Stirling (singing by Lizzy Hale)

Prince: 1999, Purple Rain

Oh, shoot. I forgot Ella Fitzgerald!

Anything by Ella Fitzgerald.

Oh! I also recommend the album Urban Flora by Alina Baraz and Galimatias. It's really calming to me, especially the song Fantasy.

The Lightning Strike by Snow Patrol

White Owl by Josh Garrels (his other stuff is great too but some of it includes rap)

Gotta go now

Cool! We have about the same music tastes! 

i LOVE ABBA; (My Dad listens to the "oldies," including ABBA all the time. :)

Some music I would suggest;

Search up Helen Jane Long. She's one of my FAVORITE piano players; and her album Porcelain is very beautiful. Her music is absolutely great to do homework to, (at least in my opinion.) Beautiful, but not to distracting.

The Piano Guys is also amazing. It's not just piano, but in their albums, they also have some violin mixed in sometimes, or they have cello. Mostly it's cello.

If you like French, I'd suggest "Les Miserables." Probably not the best thing to listen to while doing homework, and NONE of it is in French, but it IS set during the French Revoiution. (WARNING: There is a couple swear words in it; so just be careful if you do decide to listen to this.) 

Right now, that's all I can think of. If I think of any more, I'll tell you.