I think psychonauts and other good 3-D platformers will go up,simply because there aren't many. Ratchet and clank games are worth hanging on too,IMO.Even more so for 2-D platformers like Klonoa 2. RPGs and one on one fighting games have always had a trend of keeping value,and shmups too, for that matter. I can't think of any FPS that stands out as so rare and good it will be valuable,but I'm sure I am wrong.
I'm keeping all R&C,Sly cooper,and J&D games.Lots of GOW out there,but they are both SO good people will always want them.I'm also hanging on to all monster and superhero games,just because they are so big in the culture right now,and people pay for nostalgia.
I'm surprised Live and Reloaded is getting expensive, as it's heavily censored compared to the N64 original and it no longer has the "Live" option going for it, so I would think if anything the game would be dirt cheap.
One PS2 series I can see getting insanely expensive really quick is the .Hack series, parts 2, 3 and 4 are each quickly approaching 100 dollars on Amazon(and there's a collection with all 4 games that's selling for 230 dollars).
Some Xbox Games:
Dino Crisis 3
Gauntlet: Dark Legacy
Shikigami no Shiro Evolution (Red Version)
Test Drive: Eve of Destruction
Ty the Tasmanian Tiger 3: Night of the Quinkan
Xbox Music Mixer
It's one of the few Japan exclusives to not make it stateside that's absolutely awesome.
This was a stupid trivia-based game that feature girls getting naked during Spring Break. Later, it was discovered that one of the girls was actually underage during the filming so the game was discontinued. But the game had a pretty limited release already. So I'm willing to bet that this game will become extremely pricey in the future due to its rarity and explicit nature, much like the unlicensed x-rated Atari 2600 games were/are.