These are the blocks required to unlock each ship. Unless otherwise shown a ship needs the best blocks from it's predecessors also.

Science Classes:

Oberth:
Warp Core Mk 1
Phaser Mk 1
Shield Mk 1
Science Lab Mk I

Constellation:
Tractor Beam

Miranda:
Science Lab Mk V

Nebula:
Phaser Mk X
Shield Mk X
Science Lab Mk X
Warp Core Mk X

Nova:
Phaser Mk V
Shield Mk V
Science Lab Mk X
Warp Core Mk X

Intrepid:
Quantum Torpedo


Command Classes:

Constitution:
Photon Torpedo

Constitution - Refit:

Excelsior:
Warp Core Mk V

Ambassador:
Phaser Mk V
Shield Mk V

Galaxy:
Phaser Mk X
Shield Mk X
Warp Core Mk X

Soveriegn:
Quantum Torpedo

Combat Classes:

Saber:
Phaser Mk X
Warp Core Mk X
Shield Mk V

Steamrunner:

Norway:

Akira:
Shield Mk X

Defiant:
Pulse Phaser
Quantum Torpedo

Prometheus: