Both Gamespot and IGN have posted a wealth of Pre-E3 information regarding upcoming PSP games. Rather than give them all their own post, here is a good list for you to browse through.

IGN
Pac-Man World Rally
Tekken: Dark Resurrection
Metal Slug Anthology
Mercury Meltdown
World Championship Poker: All In
Star Trek: Tactical Assault

Gamespot
Tekken: Dark Resurrection
Ghost Rider
Valkyrie Profile: Lenneth
Loco Roco
Ratchet and Clank PSP
Gangs of London
Race Driver 2006
ATV Offroad Fury Pro

There are ongoing updates as well as far more than this, so be sure to check out the Gamespot and IGN main E3 pages.