Before listing the games, it is important to understand what you are downloading. Standard PSP ISOs (disc images) range from 300MB to 1.8GB. "Highly compressed" versions (usually in .cso or .7z format) achieve their tiny size via three methods:
The "PSP Minis" library is a goldmine for games under 50MB that still provide hours of entertainment: Echochrome highly compressed psp games under 200mb