I could make a shield capable of deflecting plasma and a shield capable of deflecting metallic objects today, given unlimited budget and unlimited power (but even then it would probably have minimal effectivenes).
Accelarated plasmas are either magnetically or electrically accelarated, and the reverse of the accelaration mechanism. An electrostatically charged plasma bolt (out of something like a sychotron) would be electrically charged, and so could be deflected by making the facing side of the ship charged with the same polarity. This has two problems: 1) the other side of the ship would have to be chaged with the opposite polarity. 2) it would take far more energy to stop the plasma bolt that it took to accelarate it, so you end at a disadvantage.
To accelarate a plasma magnetically would need it to be conductive (most neutral plasmas are). To fight this an inductive magnetic field causing accelaration in a different direction would be needed. this would take less energy that the electrostatic defence field, and would have the advantage of defelecting any metallic object, such as a missile or coilgun round. of course, if a bullet could be made of plastic, it would easily penetrate, as would a laser.
This is still a mass based shield (as in the sphere of metal), but for directed energy and plasmas, a low-energy plasma field may work. If this constrained to surround your ship (by magnetic and electric fields), and of sufficient density, it could absorb much of the energy from plasma (rendering it harmless), and scatter directed light, spreadign it over a larger area (again making it harmless). If greater control ofver the field was available, it could also prematurely set off the detonation of missiles (Magnetic ripples through the detonation mechanism, deflect metallic objects, and render more advanced missile harmless by causing and EMP effect, knocking out it's targeting electronics. Even exotic particles could lose energy, either by cherenkov radiation or impact catalysed decay.
Of course, all of this energy would probably be better spent pounding the enemy ship.
A better defence would be similar to that used by large Clan warships in Battletech, where a bio-mimetic system of veins in the armour pump a rapid hardening armour substitute into any hole made in the armour, so reinforcing it. It must be noted that this does not need either nanotechnology or actual biological systems, just a supply of superconcrete.
