Unfortunately, some of the Beatles' best songs--"Across the Universe," "A Day in the Life," "I am the Walrus," "Eleanor Rigby," "Within You Without You," "Because," "Yesterday," and "Hey Jude"--are ill-suited for Rock Band. And many other songs are simply not guitar driven tracks.
Anyway, here are some songs that might work (bolded songs are almost no-brainers, though not necessarily because of their quality):
Early Days (alphabetical order)
A Hard Day's Night
Can't Buy Me Love
Eight Days a Week
Help
I Feel Fine
I’m Down
I’m a Loser
I Need You
I Want to Hold You Hand
I Saw Her Standing There
I Should Have Known Better
Love Me Do
No Reply
Please Please Me
Rock and Roll Music (not a Beatles original, but still)
She Loves You
Ticket to Ride
Twist and Shout (not a Beatles original, but still)
After "Help" (alphabetical order)
And Your Bird Can Sing
Back in the USSR
Birthday
Come Together
Day Tripper
Dig a Pony
Don’t Let Me Down
Drive My Car
Everybody’s Got Something to Hide
Get Back
Girl
Glass Onion
Got to Get You into My Life (horns dominate the song, but there’s a guitar solo at the end)
Happiness is a Warm Gun
Helter Skelter
Here Comes the Sun
Hey Bulldog
If I Needed Someone
I me Mine
I'm so Tired
In My Life
It's All Too Much
I've Got a Feeling
I Want You (She’s so Heavy)
Let it Be
Lucy in the Sky with Diamonds
Nowhere Man
Norwegian Wood (no drums, Ringo used finger cymbals)
Oh Darling
One After 909
Paperback Writer
Polythene Pam
Rain
Revolution
She Came in Through the Bathroom Window
She Said She Said
Something
Sgt. Pepper’s Lonely Hearts Club Band
Strawberry Fields Forever
Taxman
The Ballad of John & Yoko
The End
Think For Yourself
Tomorrow Never Knows
Two of Us (no bass)
Wait
While My Guitar Gently Weeps
With a Little Help from My Friends
Yellow Submarine
Yer Blues
You Never Give Me Your Money