Dual analog (I think this is a given and Sony knows it) AND L2/R2 buttons
OLED screen
Built-in SS memory, even if it's just 4 GB to keep the price down, keep the mem stick slot (I'd bet games will be sold on mem sticks in the next version of PSP)
Wi-fi AND Bluetooth, can be used as a spare PS3 controller/remote in a pinch - take it to a friend's house and wirelessly transfer your game saves/share maps/RB songs temporarily/etc. Could also have some of the interfunctionality with PS3 games (limited, don't shit yourselves - say viewing the playlist on Madden) that was promised with PSP1 but won't ever happen
PSN games would come with PSP versions when you download so you can be bored by fl0w on the go
here me out here before you explode - touch screen, but it would NEVER be used for game control, EVER. It would instead be used for virtual keyboard/keypad/mouse simulation, web browsing - pc-type input, basically.
full power of the ps2 + some, downloadable ps2 games (and i think that is totally doable, and probably planned)