Judge (Whatever plastic you prefer) - Great putter for both driving and putting duties. More glide than I prefer, but matches an Atom pretty well.
Either stick with what you know and keep throwing the Core as your mid, or;
Truth - Stable enough to take more power than a Core, but not so overstable that it hooks up too quickly for a small bag.
Saint/Striker - Both should match up to a Valk pretty well, the Saint won't like wind as much as a Striker, but can be a bit longer in calm conditions.
Convict - Good, beefy driver. Great wind fighter, toward the overstable side to be used forehand or as semi-utility.
Trespass - Great disc! In Fusion, it flies very much like a Destroyer, but with a little more turn and a little more glide. Best Trilogy distance driver made in my opinion. (IE: Actually flies similar to it's numbers instead of most Trilogy which will be significantly more understable than suggested)