The Hyperion Laboratory

Explanation:
     When you accumulate enough research credits, you are presented with a choice. If you choose one item, the other item is no longer available.
So, for example, when you accumulate 5 Protoss research credits, you can choose the Ultra Capacitor.
But for the rest of the campaign, Vanadium Plating is not available. You would need to start a new campaign.
     The Laboratory is also where you have access to the Zeratul missions.

Protoss research

5 Ultra CapacitorWeapons upgrades at the Armory or Engineering Bay increase attack speed 5%
Vanadium PlatingArmor upgrades at the Armory or Engineering Bay increase life by 5%
10 Orbital DepotsSupply Depots are built instantly
Micro-FilteringRefineries produce Vespene gas 25% faster
15 Automated RefineryRefinery no longer needs SCVs to harvest gas
Command Center ReactorAllows 2 SCVs to be trained at once
20 RavenA unit built at the Starport.
Detects cloaked and burrowed enemy units
Can drop auto-turrets.
Can place Point Defense drones
Can deploy Seeker Missiles
Science VesselA unit built at the Starport.
Detects cloaked and burrowed enemy units
Can irradiate enemy units
Repairs nearby mechanical units
25 Tech ReactorCombines Tech Lab and Reactor
Orbital StrikeUnits trained at the Barracks arrive by Drop-pad
Drop-pad lands at Barrack's rally point

Zerg research

5 Shrike TurretOutfits all Bunkers with automated turret
Fortified BunkerBunker gains +150 life
10 Planetary FortressThe Command Center can upgrade to Planetary Fortress
A Planetary Fortress cannot liftoff
Perdition TurretFlame Turret which does massive area damage and conceals itself when not in combat.
15 PredatorAnti-infantry specialist unit which is built at the Factory
Periodically emits a powerful shock attack.
HerculesMassive transport ship built at the Starport.
Deploys loaded troops almost instantly.
Loaded troops survive if Hercules is destroyed.
20 Cellular ReactorSpecialist units start with +100 energy and a gain of +100 to maximum energy.
Regenerative Bio-SteelShips and vehicles gradually regenerate life
25 Hive Mind EmulatorDefensive structure that can permanently mind-control Zerg units
Psi DisruptorDefensive structure that slows movement/attack speeds of nearby Zerg units
It has a constant effect