thomaser wins this thread, hands down. That 1990 NES World Championship is all but priceless. That said, I have Shock Troopers 2nd Squad for NEO GEO AES (authentic, not a conversion or anything). Its existence was debated for a while in the early 2000's, but I assure you that it is real. Doesn't go for a whole lot on ebay, usually around $550-$600. Not bad considering that I paid ~$250 for it in 2000. I can post pics later today or tomorrow if requested.
I also have a bunch of other rare and semi-rare stuff that I don't really feel like posting. Just your garden-variety game collection stuff like mint copies of PDS, Snatcher (Sega CD), Metal Slug 3 (English AES OP), etc.
I used to have a mint sealed copy of Radiant Silvergun but I sold it 3 years ago, and I'm glad that I did. Keeping sealed copies of games is stupid IMO.
I've mostly moved away from game collecting for the time being. I'm starting to get into vinyl LP collecting; I listen to music everyday, I don't play games everyday, so it makes sense. Although I'd still like to flesh out my Saturn and NEO GEO AES collections, and add a few choice Genesis/Megadrive games. I've had my eye on Eliminate Down and Garou: MOTW for years now.