One way to quickly browse what game is available to recent platforms is to go to a site such as
www.gamerankings.com and make an advanced search.
I made a quick search with the following options:
Category: Roleplaying >> All
Platform: PSP
ESRB Rating: All
Sort By: Avg Score of Main Sites
Select a Date Range: All
Best or Worst: Best
Minimum Reviews / Votes: 5
Limit Results to: 200
Show Boxshots: List with boxshots
1. Tales of Eternia PSP Namco 10 8.6 84.310%
2. X-Men Legends II: Rise of Apocalypse PSP Activision 41 7.9 82.756%
3. Marvel: Ultimate Alliance PSP Activision 21 8.3 82.286%
4. Crisis Core: Final Fantasy VII PSP Square Enix 60 8.6 81.803%
5. Valkyrie Profile: Lenneth PSP Square Enix 48 7.9 80.604%
6. Gurumin: A Monstrous Adventure PSP Mastiff 42 7.1 79.310%
7. Brave Story: New Traveler PSP Xseed Games 33 9.0 78.530%
8. Star Ocean: First Departure PSP Square Enix 21 10.0 78.238%
9. Yggdra Union PSP Atlus Co. 17 -- 76.529%
10. Dungeon Siege: Throne of Agony PSP Take-Two Interactive 33 7.5 74.758%
Note that several games that could be counted as RPG's are listed as strategy such as Dungeons & Dragons Tactics