Crisis Core - Was actually one of my favorite FF7 spinoffs, so I would definitely recommend it.
LoH: Trails in the Sky - Haven't played this one yet, though I have played two of three of the installments of the Garghav trilogy and thought they were decent.
Z.H.P. - Haven't played this one.
One of the Ys games - The port of Ark of Nephastiwhatever has bad loading times from what I've heard, but Oath in Felghana is actually one of my favorite action RPGs ever, and Ys Seven and Ys I + II Chronicles aren't bad, either.
Star Ocean: First Departure and Second Evolution are also among my favorite RPGs ever, so maybe those as well.
Haven't downloaded anything from PSN, so I woulen't know.