Somehow I didn't get around to transfering my classic Sony PlayStation [One] games purchased from the PlayStation Network to my PlayStation Portable until recently and I'm impressed at how well they play on the small screen, so now I'm more interested in what the vintage part of the PSN Store has to offer (especially since as a Nintendo 64 booster at the time, I missed the original PS1 library entirely).  Would you care to suggest any fun games that play well on the PSP?  To avoid repetition, here's my current PS1 → PSP library:

• Castlevania Chronicles
• Castlevania: Symphony of the Night (via Castlevania: Dracula X Chronicles)
  
• Spyro the Dragon
  
• Street Fighter Alpha

What say you, gang?  Any suggestions?  What must-play adventure am I missing?  Platformers preferred, naturally.