Samples aside, summertime is one of the most covered songs in recorded music history. Perhaps you recognize it from another version of summertime.

"April in Paris"
is classified as jazz standard,
a song composed by Vernon Duke with lyrics by E. Y. Harburg in 1932 for the Broadway musical, Walk A Little Faster. The original 1933 hit was performed by Freddy Martin, and the 1952 remake (inspired by the movie of the same name) was by the Sauter-Finegan Orchestra, whose version made the Cashbox Top 50.

It has been performed by many artists, including Louis Armstrong, Count Basie, Bill Evans, Charlie Parker, Coleman Hawkins, Frank Sinatra, Mary Kaye Trio, Billie Holiday, Sarah Vaughan, Thelonious Monk, Ella Fitzgerald , Benny Goodman, Dinah Shore, Glenn Miller, Doris Day, Errol Garner Trio, Alex Chilton, Tommy Dorsey, Blossom Dearie, Wynton Marsalis, Sal Viviano, and Dawn Upshaw. Basie's 1955 recording is the most famous, and that particular performance was inducted into the Grammy Hall of Fame. On this recording, trumpeter Thad Jones played his famous "Pop Goes the Weasel" solo, and Basie directs the band to play the shout chorus "one more time," then "one more once." The song is also featured in the film Blazing Saddles.

Http://en.wikipedia.org/wiki/April_in_Pa…

Some suggested jazz standards:

All The Things You Are
My One And Only Love
Body And Soul
There Is No Greater Love
Just Friends
In The Wee Small Hours
Some Day My Prince Will Come
These Foolish Things
Summertime
Georgia On My Mind
All Of Me
On The Sunny Side Of The Street
Memories Of You
Love Is Here to Stay
Confessin'
But Not For Me
Just One Of Those Things
My Romance
In A Sentimental Mood
Easy Living
The Nearness Of You
Over The Rainbow
Darn That Dream
I Didn't Know What Time It Was
Embraceable You
Autumn In New York
Sophisticated Lady
They Can't Take That Away From Me
Alone Together.

Ella Fitzgerald was a wonderful singer and it's not easy to mention another singer who could be similar to her. I would suggest that you add Billie Holiday to your listening and Sarah Vaughn. The Billie Holiday small group stuff she did on the Verve label swings. Her recording of Stormy Weather is the definitive one.

For male swing era vocalists I would suggest the Joe Williams era of the Count Basie orchestra in the 1950s, maybe get a sampler of Louis Jordan (fun, funny swing tunes with titles like "What's the Use of Getting Sober When You're Going To Get Drunk Again") and even some Cab Calloway. Bing Crosby did a number of very nice recordings of swing numbers. His career lasted so long and covered so much different ground that you'll need to seek out the swing era stuff, but he did do records with Jack Teagarden, Eddie Heywood and Jimmy Dorsey. Also, look for Glen Miller Orchestra recordings with Ray Eberle as vocalist – very nice swing music.

Tony Bennett is not really a swing vocalist, I would skip him. He kind of came after the swing era and he would be likened more to the "Vegas era" Sinatra.

If you want to go a little earlier, like "pre-swing", mid-1930s era "dance bands" (before the swing era was really given that name of "swing"), check out the Ray Noble Orchestra, particularly with Al Bowlly as vocalist. There is a recording which is a real favorite of mine, it's the "Ray Noble and his American Orchestra" recording (http://www.amazon.com/Ray-Noble-His-American-Orchestra/dp/B0000W3Z6E) which has mostly vocal numbers and with a couple of different singers, doing great renditions of songs like "Top Hat, White Tie And Tails", "Nice Work If You Can Get It", "I've Got You Under My Skin" and "I've Got My Love To Keep Me Warm", among others. It's a real favorite recording of mine.

I hope this helps!