OutRun 2006 (flame rings in 4th level on the left, 4 morph weights IIRC)
Depth buffer reads from the CPU
Midnight Club: LA (sun lens flare)
Syphon Filter (light halos (lots per frame!))
WipEout (sun lens flare). Multiple reads per frame to get an average.
a few more
Direct color buffer reads from the CPU
Coded Arms: Contagion (reads a single pixel from the alpha/stencil channel to identify enemies to lock-on)
Dangan Ronpa, Dangan Ronpa 2 (renders a separate mini buffer to select clues, people)
MotorStorm: Arctic Edge (light adaptation)
a few more
Color buffer format aliasing
Cars Race-o-rama
OutRun 2
Split/Second
Spongebob
Depth buffer manual swizzling through geometry
This is a mistake that a few games have made - the PSP has hardware to swizzle depth buffers to linear, but instead they use triangles to simulate the swizzle to match. This applies to the particle effects in these games:
Tales of Phantasia X/Cross Edition (included as a retro game in Tales of Phantasia: Narikiri Dungeon X), see issue #21098
Block copies to RAM, later used as texture
Burnout Legends (sun lens flare)
Digimon
Tales of Phantasia X
CLUT lookups from color framebuffers ("depal")
Dragon Ball Z: Tenkaichi Tag Team
Test Drive (with "smooth" lookup workaround for better color precision)
Burnout Dominator (lens flare effect)
Tantalus games (Spongebob, etc)
Many more
CLUT lookups from depth buffers
Fog effect in Katamari Damacy
CLUT lookups with palette in framebuffer
Ridge Racer 1/2 (digital speedometers)
Reinterpret color framebuffers
Outrun 2006 (however, worked around with "BlueToAlpha" method)
Split/Second (however, worked around with "BlueToAlpha" method)
Tantalus games (Spongebob, etc)
Memcpy framebuffer download/upload
Everybody's Golf 2 (line by line, ugh)
Zipped PRX
Fired Up
Persistent render targets
Mahjong Artifacts (Minis) relies on render targets sticking around.
"3D textures" using malformed mipmap chains
The PSP doesn't have any restriction on the size relationships between successive mipmaps in a pyramid. Hence, it's possible
to put multiple images of the same size into the mipmap layers of a texture, and use trilinear filtering to interpolate between them.
Usually, for control, the mip level is controlled directly (instead of automatic from screen-space derivatives).
This is used by the following games:
Macross series games (water effect, see #6357)
Misshitsu no Sacrifice (background animation, also see #6357)
Tactics Ogre: Let Us Cling Together (JAP/CN-patch) (font atlas, see #5350)
As far as I know, no other games use a "malformed" mip chain like this.
In Tactics Ogre it's to fit a lot of characters in a single font texture (for no good reason, really). In this case, every two successive mipmaps points to the same texture page, for a total of four. Not sure why it's done this way.