Earthbound for the SNES (I have it) is worth a lot these days. Amazon has it at almost 200 for used.

I know my copy of Metroid II:RoS on the Gameboy is worth over $100.

Took forever for me to find it, tho was only $4 in a bargin bin.

No desire to sell it though.

Here's a short list of some of my most valuable games:

US Releases Only - No Imports

Panzer Dragoon Saga (Sega Saturn)
Chuck Norris Super Kick (Atari VCS)
Golden Axe Warrior (Master System)
Chrono Trigger (SNES)
Project Justice (Dreamcast)
Metal Gear Solid (Gameboy Color)
Phantasy Star 2,3 & 4 (Genesis)
Legend of Zelda 4 Game Collection (GCN)
Final Fantasy VII Black Label (PSX)
Action 52 (Genesis)
Bomberman 64 The Second Attack (N64)
Burning Rangers (Sega Saturn)
Steel Battalion with Controller (Xbox)
Snatcher (Sega CD)
Cannon Spike (Dreamcast)
Donkey Kong Circus (Game & Watch)
Shinning Force III (Sega Saturn)
Castlevania Legends (Gameboy)
Alex Kidd in Shinobi World (Master System)
Halo Triple Pack (Xbox)
Ico (PS2)
Boarder Down (Dreamcast)
Lunar 1 & 2 (Sega CD)
Mass Effect Limited Edition (Xbox 360)
Popful Mail (Sega CD)
Metal Gear Solid: The Twin Snakes (GCN)
Shining Force I & II (Genesis)
XenoGears Black Label (PSX)
Magic Knight Rayearth (Sega Saturn)
Outrun 2006 Coast 2 Coast (Xbox)
ToeJam and Earl (Genesis)
Legend of Zelda Ocarina of Time / Master Quest (GCN)
Lunar 1 & 2 (PSX)
Mars Matrix (Dreamcast)

Most of these will be hard to find because they are rare. I do suggest that you try to play any you find because most of these are real gems. Panzer Dragoon Saga is one of my all time favorite games. If you do find it for a great price don't let it go without at least playing through it once.

MVC2 on ps2 is pretty rare. Suikoden 2 is very rare as well.

And? Have you got something good from the flea market?

I know it's too late now, but for future reference;
NES games generally are worth the most. This is because it is the most popular system to collect for. Most Nintendo first party titles hold at least their value like forever, except those that sold huge which would be cheaper because they're common.
As a rule, games on Nintendo systems are a safer purchase, but some SEGA and Atari games can be worth a good amount too.

I don't know how much is rare to you, but I was shocked how much a new copy of Valkyrie Profile was worth.

http://www.ebay.com/itm/Valkyrie-Profile-PSX-Playstation-NEW-SEALED-RARE-/150891460936?pt=Video_Games_Games&hash=item2321d4f948

Suikoden II

We're going this Sunday.  I'll keep you posted.