A is for Annorax and his mighty temporal weapon.
B is for the Borg Collective, which originates from and has its base within the Delta Quadrant.
C is for Chaotic Space. Voyager encountered a patch of it there.
D is for... something other than Delta Quadrant.
E is for Enara Prime, a planet encountered by Voyager.
F is for False Profits.
G is for the Gift of 9500 light years, given to Voyager by Kes.
H is for the Haakonian Order, which in the 2350s conquered Talax and engaged in a decade-long war with the Talaxian people.
I is for Interplexing Beacon. Which Borg marooned in the mid-21st century attempted to use to contact the Borg Collective in the DQ.
J is for Janeway, her and her crew were stuck there for a time.
K is for the Kazon. Of all stripes and affiliations, Nistrum or otherwise.
L is for Lokirrim, who used photonics (holograms) as servants.
M is for Malon, another species native to the quadrant.
N is for Nekrit Exapanse. One of the prettier areas of the DQ.
O is for Omega Particle, located by Voyager in the Delta Quadrant.
P is for Picardo, Robert. One of the highlights of Voyager. & Phage, a rather nasty epidemic that did a number on the Vidiians.
Q is for, well Q, because he showed up there too.
EDIT: Because Saty beat me to the punch with P.