The PS3/PSP store will be closing in July with the Vita one closing in August.

My recs...Getting these out of the way pretty much ALL Square and Enix titles then Atlus PSOne/PSP/PS2 Classics.
After this, Popolocrois 1 and 2 on JP PS store as well as Sega Ages 2600 PS2 remakes with Phantasy Star 1 and Fantasy Zone. Both of these are PS2 classics on the JP PSN with Fantasy Zone being a remake of Super Fantasy Zone as if it had been developed on the Fantasy Zone arcade board, go M2!!!
Those are it so far but I''ll find more games on JP PSN store to recommend.

Feel free to add some, I just mentioned these as they aren't super obvious rare ones.