Non-exhaustive list:

NPJG90001 # LocoRocoダウンロード体験版 (Christmas)
NPJG90002 # LocoRoco™ おためし版
NPHG00005 # Echochrome PSP
NPIA00013 # SensMe™ channels
NPJG90003 # Doko: Lets Gakkou
NPJG90009 # Yuusha no Kuse ni Namaikida
NPJG90011 # Patapon
NPJG90019 # Echochrome PSP
NPJG90020 # Bleach Heat The Soul 5
NPJG90041 # Bleach Soul Carnival 2
NPJG90042 # Bleach Heat The Soul 6
NPJG90047 # Everybody's Sukkiri
NPUG80318 # LocoRoco Midnight Carnival
UCAS40063 # LocoRoco™ download trial version
UCED90007 # LocoRoco Christmas Demo
UCED90042 # SOCOM: Fireteam Bravo 2
UCES00001 # WipEout Pure
UCES00302 # Ape Academy 2
UCES00304 # LocoRoco™ Halloween
UCJS05232 # Lumines ll
UCJS10032 # サルゲッチュ ピポサルレーサー
UCJS10036 # Kazuo
UCJS10041 # LocoRoco™ download trial version
UCJS10043 # Tama Run
UCKS45020 # LocoRoco™ Halloween
UCUS98662 # LocoRoco Downloadable Demo
ULED90018 # Mercury Meltdown
ULED90043 # Xyanide Resurrection
ULJM05126 # Kawashima Ryuuta Kyouju Kanshuu Nouryoku Trainer Portable 2
ULJM05135 # 脳に快感 アハ体験!
ULJM05161 # Exit 2
ULJM05164 # Dungeon Explorer : Meiyaku no Tobira
ULJM05168 # 視て聴いて脳で感じてクロスワード天国
ULJM05184 # Homestar Portable
ULJM91014 # ファンタシースターポータブル
ULJS00021 # Bounty Hounds
ULJS00068 # Blokus Club Portable with Bumpy Trot
ULJS00105 # Mawaskes Based on Carton Kun
ULJS00141 # Ikuze! Gen-San : Yuuyake Daiku Monogatari
ULJS00159 # Sengoku Efuda Yuugi: Hototogisu Ran
ULUS10289 # Dungeon Explorer: Warriors of Ancient Arts

The oldest game demo

Looking at NPJG90001, it seems to be the oldest demo because PARAM.SFO requires minimal FW 2.70. DATA.PSP is about 8 MB. There is no DATA.PSAR. That means this is the type of demo where there is only an executable in DATA.PSP and no DATA.PSAR.