No shower singing for me. So it's usually singing whatever pops into my head to the pups. Which might be kid songs (e.g., "You are my sunshine", "Clementine", "Bananas in pajamas"), pop songs (OK Go's Needing/Getting and Blue October's Calling You are recent examples) or any silly song made up song about the pups that my brain puts forth. Good thing I can carry a tune :)

ONLY in the shower:

Here Comes the Sun

Suzanne

Leaving on a Jet Plane

and a whole bunch of songs I learned in Girl Scout camp. I really should have been told I'd have a lifetime set of ear worms.

I think a better question, what songs DON'T I like to sing without any recording playing in the background? And what songs do I particularly like to change the lyrics to to make them about my dog and/or cat?

The intro to Rye Whiskey/Time to Switch to Whiskey:

Rye whiskey, rye whiskey, rye whiskey I cried
If I don't get rye whiskey well I think I may die

I'm gonna go up beyond the holler, gonna build me a still
And I'll sell you a gallon for a five dollar bill

Well if the oceans was whiskey and I was a duck
I'd swim to the bottom and never come up

But the oceans ain't whiskey, and I ain't no duck
So I'll play the jack of diamonds and trust to my luck

Jack of diamonds, jack of diamonds, I know you hold
Deprive my poor pockets of silver and gold

Well it's beefsteak when I'm hungry, rye whiskey when I'm dry
Greenbacks when I'm hard up and heaven when I die

Rye whiskey, rye whiskey, rye whiskey I cried
If I don't get rye whiskey well I think I may die

Well my horses ain't hungry and they don't want your hay
Fare thee well darlin' I'll be on my way

"Lily, Rosemary, and the Jack of Hearts" by Joan Baez, originally written by Bob Dylan.

And a quirky song I learned on Dr. Demento, "The Scotsman". Both are too long to post here, I think.

Opera (mostly Mozart). Nobody makes fun of my terrible runs in my happy place!

Wait, that sounds icky...

Redvixen, I impressed that you can remember the words to "Lily, Rosemary, and the Jack of Hearts"!

I am impressed, that is.

Her name is Minerva Ouch
A cowpuncher's dream come tr-tr-tr-true
Her looks don't amount to much
Cuz one of her eyes ain't bl-bl-bl-blue
Well, her skin is like prairie dog leather
And all she can make is her chuck wagon stew
Her name is Minerva Ouch
She's the flower of Gower Gulch

Thank you, thank you.

I will sing all kinds of crap just to freak people out.
Except now people burst out into song all the time, so it's lost all flavor.
I've stopped encouraging people to sing as well.
It use to just be me and Jeff Goldblum. Now everyone's expecting a flashmob to start.
Sigh.

I'm more of a "dance to the music only I can hear" person than a singing person.

My bologna has a first name, it's O-S-C-A-R
My bologna has a second name, it's M-A-Y-E-R
Oh, I love to eat it every day
And if you ask me why I'll say
'Cause Oscar Mayer has a way with B-O-L-O-G-N-A

(Yes, I grew up watching way too much TV.)

I'll also sing "My Only Sunshine", "Scarborough Fair", "Over the Rainbow" and "Leaving on a Jet Plane". I know only a few words of the latter two songs, so I tend to repeat the same words over and over.

I found it. Wow, I don't know how long it's been since I've seen it. I'm surprised I was so close.

For the past week or so? Afternoons & Coffeespoons by the seriously underrated Crash Test Dummies.

I sing a lot but I have a few favorite shower songs. "I Dreamed a Dream" from Les Miserables is awesome because you can really belt that one and benefit from bathroom reverb. "Son of a Preacher Man" works for that, too.

Basin Street Blues. I do this version and I do the trumpets and the Ella/Satchmo parts as well. Very satisfying shower song, actually. Or I pull out my best Pavarotti impersonation (which isn't bad for a girl) and sing Nessun Dorma.

To the pets, when they exasperate me:

You will never understand
How it feels to live your life
With no meaning or control
And with nowhere else to go. . . .

I have a directory with 110 songs I like to sing. It's not with every song that the lead vocal alone can stand alone.
Examples:
Robert Cray - Right next door
Phil Phillips - Sea of Love
Righteous Brothers - You've lost that loving feeling
Harold Melvin & the Blue Notes - Don't leave me that way
Gram Parsons - Love hurts
Nat Cole - The very thought of you
The Platters - The great pretender

Schubert - Winterreise, Erlkönig
Rameau - Fatal amour

Singing them without something playing in the background helps you hear your own timbre.

When I first hear a song that's suitable for singing I find myself playing it again and again for a while. Like the 'impregnation fase' of a new relationship. And then I know the melody and lyrics. Like recently.

I do "Within You / Without You" but not so much singing, more as a breathing exercise and meditative moment.

This if I'm cheerful. Also, this. When I'm feeling determined, this. All after checking carefully to make sure roommates have left for the day. Excellent shower songs.

Big Bottom - Spinal Tap

The bigger the cushion, the sweeter the pushin'
That's what I said
The looser the waistband, the deeper the quicksand
Or so I have read

My baby fits me like a flesh tuxedo
I'd like to sink her with my pink torpedo

Big bottom, big bottom
Talk about bum cakes, my girl's got 'em
Big bottom drive me out of my mind
How could I leave this behind?

I met her on Monday, 'twas my lucky bun day
You know what I mean
I love her each weekday, each velvety cheek day
You know what I mean

My love gun's loaded and she's in my sights
Big game is waiting there inside her tights, yeah

Big bottom, big bottom
Talk about mud flaps, my girl's got 'em
Big bottom drive me out of my mind
How could I leave this behind?

My baby fits me like a flesh tuxedo
I'd like to sink her with my pink torpedo

Big bottom, big bottom
Talk about bum cakes, my girl's got 'em
Big bottom drive me out of my mind
How could I leave this behind?

Yeah, Scarborough Fair and Over the Rainbow here too. Shower sisters, deborah!

Bridge Over Troubled Water (S&G), With or Without You (U2), pretty much anything from Achtung Baby (U2), and This is the Last Day of Our Acquaintance (Sinead O'Connor).

It changes from day to day, year to year, of course. Just last night I was singing "Do You Wanna Hold Me," a Bow Wow Wow song that I probably hadn't heard since the 80s, until the recent one-hit wonder thread sent me down the YouTube rabbithole.

But a few perennial favorites, which I mostly belt out while I'm doing the dishes:
- Stormy Weather (though my range is more Keely Smith than Lena Horne)
- Reno Dakota or Kiss Me like You Mean It by the Magnetic Fields
- and the all-time doing-the-dishes chart topper for the past five years or so: Ronnie Dobbs' aria, "How High the Mountain," from "Fuzz The Musical", Mr. Show's fictional (and later, actual) movie musical spun off from the fictional reality show "Fuzz." Yup. [NSFW: language]

Ha, I see a lot of you find your songs in the camp fire genre (John Denver, S&G).
I'm very impressed with NQMAs choice of Verdi and Vivaldi. I've never sung any Italian.
Do you sing Rusalka in Czech?


Stormy Weather sounds perfect. I found a lot of songs like that through the soundtrack of The Singing Detective. Like After you've gone, Accentuate the positive, You always hurt the one you love, etc.
I've only discovered the Magnetic Fields recently; it's fun to do the resonant bass bariton.