I'll happily sponsor a game port or fresh development for 100-250quid if itt's a game I like. If anything the amount isn't enough as that is a significant amount or work. If they were really lucky and sold 1000's of copies at a few quid a pop then I'd hope they'd return my investment.

As for which game, well this is an interesting issue. Q3A is a very good example of the quality gfx, 3d, speed and sound playback for the n900 and even had a reasonable effort put in to controls. Sadly you find ultimately solitaire or bounce win because this is a 10cm long device held in your hand. Orienation and touch sort of work but you reall just want keyboard controls for anything other than bounce or zenbound. I would recommend somebody ports Pandemonium. This is graphically and visually stunning with fun game play with only left/right and jump keys required.
There are probably other games with 3 or so keys needed but that are engrosing. These should be ported.