Depends if you want to make a profit now or invest in the future...
Any of the Nintendo first party games tend to hold their value, Mario, Pokemon, Metriod, Zelda and Kirby.
I don't think any of the current gens games have gone up in value since release and it's hard to forecast a future classic but RPGs tend to be the biggest genre people collect with adventure games selling at a higher price.
Look for games that have limited release numbers normally done by smaller publishers such as Atlus or really high rated games that sold badly like The Puppeteer. Even a game like Catharine may sell for stupid amounts in the future as everyone tends to have it as a ps+ free game rather than the disc.
Games collecting for a profit is a crazy idea as publishers can release a game as a download and crush the market overnight like they did with SOTC/ICO but they will always be the hardcore collector that wants the disc/manual/box. Luckily I only buy games I intend to play.
Collectors/Special editions are the worst for making cash, they cost loads, everyone is saving a mint copy for sale and the collector your trying to sell it to has already got it. The only exception to this, is IF it's truly a limited or numbered release of the game. The other is if you want a quick turn around; say 3-6 months after release when the collectors themselves have missed the release and they are hitting flebay to try and get hold of the game. Limited/Special edition consoles do sell for stupid prices but tend to have to be mint.
If you want to walk out of blockbuster and straight into CEX, the only thing I can suggest is to take a smart phone and bring up their buy prices. The chances are that what ever your selling to them will sell for more on flebay, it's their business to know the prices of games and they are pretty clued up. I would go to the shop your selling to first and have a quick scan around and look for the games that they don't have or have very few copies of, then go to blockbuster and see what they have.
Stay away from sports games, they are the pits as a new version comes out every year.
