Border Down is a masterpiece, but it goes for $150-$200 now, so you may have missed the "worth picking up" boat. Under Defeat is likewise one of my favorite DC games(
review). I think you can still find that one, and its well worth the $60.
Radirgy is good, but it's coming to the GC in the US for cheaps. Trizeal is alright, especially if you like Raiden/Shienryu style shooters, but IMO not worth dropping $60 on. You're better off skipping Chaos Field, but it's cheap on the GC in the US if you're curious.