Actual Solos:

Season 1: True Colors

Season 2: I Follow Rivers

Season 3: Because You Loved Me

Season 4: Gangman Style, I Don't Know How to Love Him,
Hung Up

Duets:

Season 2: Sing!, Dog Days Are Over

Season 3: L-O-V-E, Flashdance... What a Feeling


Solos in a Group:

Season 1: Push It, Proud Mary, My Life Would Suck Without You, Express Yourself, Bad Romance, Give Up the Funk, To Sir With Love

Season 2: Toxic, One of Us, Time Warp, Start Me Up/Livin on a Prayer, Marry You, The Most Wonderful Day of the Year, We Need a Little Christmas, God Rest Ye Merry Gentlemen, Deck the Rooftop, Born This Way, Pure Imagination, Light up the World

Season 3: America, I Can't Go For That/You Make My Dreams Come True, ABC, Do They Know It's Christmas?, Summer Nights, First Time Ever I Saw Your Face, Cell Block Tango, Shake it Up, Edge of Glory, In My Life

Season 4: Call Me Maybe, Womanizer, 3, Some Nights, Don't Dream It's Over, This Is the New Year, Diva, Wannabe, I Love It

"Blaine has sung in at least one song in twenty-one of Season Four's twenty-two episodes, the most of any other character in a single season." (link)
I can't even list all of Blaine's solos because he has so many... Possibly as many as Rachel. And Let it be known that Blaine only joined ND in season 3.

Marley Solos.

Actual Solos: Chasing Pavements, Everytime, Look At Me I'm Sandra Dee (Reprise), The First Noel

Duets: New York State of Mind, Crazy/You Drive Me Crazy, Blow Me(One Last Kiss), Holding Out for a Hero, Tell Him, Locked Out of Heaven, A Thousand Years, You're All I Need to Get By, Diamonds Are A Girl's Best Friend/Material Girl, All or Nothing

Solos in a Group: Womanizer, Born to Hand Jive, you're The One That I Want, Some Nights, Don't Dream It's Over, Have Yourself a Merry Little Christmas, This is the New Year, We've Got Tonite, Anything Could Happen, Wannabe, Mamma Mia, Say, You Have More Friends Than You Know, Outcast, Longest Time, Superstition.

The amount of solos in a group Marley has had in season 4 alone is the same amount Rachel has had in season 1 when the show first started. Marley just joined ND.

I know I ranted about this in the beginning of the season but this really needs to be known. It's not fair that a well liked character who's been on the show since the beginning is shoved to the back to make room for the newbies. Same goes for Artie but he hasn't been used as a human prop as much.
And the only time Tina got a solo at a competition, Marley fainted at the end!

So I just wanted to make my point clear that it's not fair at all that characters like Blaine and Marley, who aren't original ND members, get so many solos and screentime.