What cool 2nd 3rd and maybe 4th specs would compliment the explorer's signature talent to spend 2 (or 1 with the upgrade) dp's to get 3 maneuvers, with upgrades free of strain...

All of them?

Seriously though, everything benefits from additional (free) manoeuvres. Whether it's because you have abilities that can activate with manoeuvres, or you have strain-expensive abilities that would benefit from you not having to spend strain, and so on.

Well ok... Sure. But what I'm looking for is things that take advantage of being able to move twice every round or manuever talents that do fun things.

I have 890xp that I'm trying to spec with around unmatched mobility.