When I started collecting a few years ago, Imagic games were my favorite (for awhile). I actually stumbled blindly into my boxed copy of Subterranea. I was at a Flea Market, and a very nice lady was unloading all of her games from various classic consoles for $5 apiece. They were all boxed, complete, and in near-mint condition. It was probably my biggest collecting score.
2600: Dragonstomper
Intellivision: AD&D- Treasure of Tarmin
Colecovision: Gateway to Apshai
Atari 7800: Midnight Mutants
Commodore 64: The Bard's Tale
NES: Dragon Warrior 1,2, and 3 , Crystalis
SMS: Phantasy Star
Atari ST: Dungeon Master, Dungeon Master: Chaos Strikes Back
Genesis: Phantasy Star IV, Shining in the Darkness
SNES: Never played any that long, but so far, Chrono Trigger
Turbografx: Dungeon Master- Theron's Quest, Y's: Books 1 &2
Sega CD: Dungeon Master 2 - Skullkeep, AD&D- Eye of the Beholder
Lynx: Daemonsgate
Game Gear: Defenders of Oasis
We actually told her she could get a bunch more money if she sold it on e-bay or something, but she just wanted to get rid of all of her stuff as quick as possible. We got a jackpot of near-int boxed complete games for a bunch of systems for $5 each. Subterranea for the 2600, Fathom for the Intellivision...it was definitely our best score in the wild.