I'm a newbie to the genre and only own a few: Dragon Spirit: The New Legend, Sky Shark, and Stinger. I want to get many more because they tend to be fairly cheap and I like NES controls. What games are best, what are the worst, and do any feature hot anime girls?
EDIT: Official List compiled throughout this thread
Currently at 64 titles:
1942
1943
Abadox
AD&D Dragon Strike
Adventures of Dino Riki
Alpha Mission
Burai Fighter
Captain Skyhawk
Crisis Force
Double Strike
Dragon Spirit
Exed Exes
Fantasy Zone
Galactic Crusader
Galaga
Galaxian
Galg
Gradius
Gradius 2
Guardian Legend
Gun.Smoke
GunNac
Gyruss
Image Fight
Isolated Warrior
Kings Knight
Legendary Wings
LifeForce
Lock 'n Load!
Macross
MagMax
Metal Fighter
Millipede
Mission Cobra
Over Horizon
Parodius
Recca
SCAT
Section Z
Silkworm
Silver Surfer
Seicross
Sky Kid
Sky Shark
Spy Hunter
Sqoon
Star Force
Star Soldier
Starship Hector
Stinger
Super Spy Hunter
Tale Spin
Terra Cresta
Thunderbirds
Thundercade
Tiger Heli
Twin Cobra
Twin Eagle
Twinbee
Volguard II
Xevious
Xexez
Zanac
Zombie Nation