I don’t know if you can buy SoTN standalone, but it’s included in Castelvania Dracula X Chronicles, along with the original and re-made Rondo of Blood. It’s a nice Castlevania package, well worth it.
I’m playing Valkyria Chronicles 2 now, which I’d recommend, with the caveat that the story it pretty anime-y. But the gameplay is completely solid.
My understanding is that the strategic elements of Patapon 2 are better than the first, but I didn’t enjoy the first especially.
I think the second one is supposed to be more accessible, but yeah this was a game I wanted to like more than I did. The art and music are top notch, I’m just not good at the game.
I’ll throw out Mega Man Powered Up and Maverick Hunter X as games worth playing. I’m genuinely sad we didn’t get more games like them on PSP.
I’m currently playing Ys: Oath of Felghana, which is a remake of Ys III. I like it, though the boss fights are too tough! I’d be ok, but the thumbstick hurts my thumb when I play too long, and the boss fights are intense. Luckily, if you lose a few times, it lets you temporarily lower the difficulty, which I do so that I can move on :). But I like the game.
A lot of good recommendations already, so I’ll just second FFT.
Just replayed Marvel Trading Card game this morning. I almost forgot how absorbing the SP component of the game. I think you can easily find the game in the bargain bins nowadays.