One rare nes game is Stack-Up. Only a limited number was ever produced. I actually used to own one myself. Back in '89 xmas I recieve a nes bundled with R.O.B. Stack-Up, Gyromite, and Duck-Hunt. Parents bought off a clearance sale for $99.
Duck-Hunt was a plus, but I was really disappointed when I got it because it didn't included Super Mario Bros.
The Stack-Up game is by far the most useless nes game I have ever played, you can only play it if you have R.O.B. I stored Stack-up, Gyromite, and R.O.B in a closet until I sold it all on ebay back in 2002.
I didn't expect anymore than $80, but the auction ended at $306. A friend of mine told me the driving force of the auction was Stack-Up because I was selling it complete and in mint.