In Collecting

I sold off most of my collection last year like an idiot and now I'm back into collecting them again. I still have:

Legend of Zelda (Grey cart)
Castlevania 1 & 3
Ninja Gaiden II

What are some of the must have games I'm forgetting?

Mighty Final Fight
Mike Tyson's Punchout
New GhostBusters II (PAL)
Super Dodge Ball
Crash & The Boys Street Challenge
River City Ransom
Contra
Megaman 1-6
Ninja Gaiden 1 & 3
Bonk's Adventure
Metroid
Teenage Mutant Ninja Turtles 2 & 3
Double Dragon
Super Mario Bros. 2 & 3

I just bought Mighty Final fight, Crash & the Boys, and Zelda II: The Adventure of Link (Grey cart ) on ebay to start me off.

am I forgetting any must have games?

Here's some:
Kid Icarus/SMB 1 (should be really easy to find that one)/Final Fantasy/Ultima Exodus/Ice Climber/Balloon Fight/Excitebike/Donkey Kong Classics/Maniac Mansion/Adventure Island.
And those are ones I can think of just right at this moment. And no respectable NES collection is complete without a gold Zelda cart. Or two.

Castlevania II

Well, I'd say you should get SMB for sure, personally I like the original Teenage Mutant Ninja Turtles game and Bionic Commando. Abodox is also a great game in my opinion, so from me it's a must. Chip'N'Dale Rescue Rangers 1 and 2, Metroid, Balloon Fight and Deja Vu.

That's really all that comes to mind right now.

Shadowgate