Alphabetically by title, "Abacab" by Genesis is sixth.

Beating it are:
"A-Tisket, A-Tasket" - Ella Fitzgerald
"'A' - You're Adorable" - Perry Como
"A&E" - Goldfrapp
"Aah-Ah, Yawa Em Ekat ot Gnimoc Er'yeht" - Vix Noelopan
"Aba Daba Honeymoon" - Arthur Collins & Byron G Harlan
At the end of the alphabet are three songs with no titles at all (by They Might Be Giants, Ryuichi Sakamoto and the Art of Noise). I have a bunch of songs with numbers in them, too, as well as several in Japanese (which apparently go at the end of the alphabet). The last ones that actually start with Z are
"Zombies Ate My Neighbors" - Single File
"Zonky" - Fats Waller
"Zoo Kicker & I" - Dead Bubbles
"Zorba the Greek" - Herb Alpert & the Tijuana Brass
"Zorro" - The Chordettes
And just because I'm already organizing...
Band name:
The A's
!!! (or ZZ Top if it's alphabet only)
Album Name:
The A's (by the A's)
Zzyzx (by Zeromancer)
Time:
"St John's Passion: Recitative (Evangelist)" - Johann Sebastian Bach
"Nagasaki (breakdown)" - Fats Waller (both 4 seconds)
"Blue Room" - The Orb (40:00)
Last Played:
"The Aircrash Bureau (live)" - Gary Numan (about an hour ago)
"Well Well Well" - Woodentops (August 20th, the day I reinstalled iTunes)
Count:
"Omobolasire" - Prozzak/Simon & Milo (14)
several thousand tied with zero plays
Lex