I'd have a hard time believing Zero Mission to be rare.
I think the Japanese versions of the Metroid GBA games maybe, but not the English versions. (supposedly Fusion only sold about 180k in Japan, but over a million in NA)
(I know the JP version of Fusion has an ending photo viewer, as well as an unlockable Hard mode as well and probably a couple other ending images to unlock.
However, I don't think the JP version of Zero Mission has any content differences that would make it interesting to import fans (even the unlockable Metroid is still the NES version rather than the FDS version).

Earthbound, Sword Of Hope and Zero Mission. All Sealed, All Mine.

And I ended up paying a fortune for Lunar anyways. Ah well, at least I grabbed Gunbird 2 along with it for just $25.

1990 Nintendo World Championships Competition NWC Gold Cartri...

Tempting to take out a second mortgage.

I payed just under a 100$ (no shipping or handling fees) to buy a used Metroid Prime Trilogy Collectors Edition in very nice condition (the case is perfect, but there is a fold on the instruction booklet and also a smudge on the art-book, although neither faults are noticeable). On the internet, I've seen the disc alone go for almost the same price, so was this a good deal? I don't know much about video game collecting, I was just wondering if I got a bargain.

And I ended up paying even more for Lunar 2. Twice.

Wow $27,000?

As for rare games, I do have a copy of Pokemon Green, although I'm not sure that it's particularly rare.

@Captain_Balko: As for the Metroid Prime Trilogy, that game has a huge variance in price. I say $100 for a used complete copy is pretty good. I think that is close to about average at the moment. That reminds me, one of these days I am going to have to try out my copy on the Wii U.

How much is a Famicom-theme Game Boy Micro? _{Not that I'd actually sell it...}

@Nobodys_Angel: Here's some of the latest sales. Depends on condition and what all is included like the box, etc.
http://www.ebay.com/csc/i.html?_sop=10&_sacat=0&_from...

@Ryno I see, thank you

Man speaking of Metroid Prime Trilogy, what's up with the huge prices on a lot of out of print games for Gamecube and Wii? Guess there's a lesson to be learned here and I'll have to get the good stuff for the Wii U as it is coming out. Nintendo will always be popular with collectors I suppose.