Legends, Beast Wars, and other wants.
 

Titans Return:
Rumble (yes, I never found one)


Takara legends:
Rewind
Targetmaster Windblade/Caliburst
Magna Convoy


Transformers Adventure:
Windblade

Beast Wars:
Either the American or Japanese Anniversary versions of Ultra Optimus Primal and Megatron, with retooled heads.
Telemocha Dinobot (with painted mouth)

Henkei:
Dinobot


RID '01:
Spychangers, both Gobots molds and original-mold minifigures
The Machine Wars flipchanger repaints (Skids, Tow Line, Wind Sheer, Skyfire)
Team Bullet Train (must be in good condition and unbroken)
Ruination (Original release, none of the camo versions)
Megatron Megabolt

Reissue:
G2 Battle Convoy/Laser Optimus reissue.