Just my thoughts on extending the tech tree out with some changes. All these typically include the prerequisite alien artifact as well (So Plasma Pistols will need you to have a Plasma Pistol).
Alien ContainmentResearch Required: Any alien corpse
Mind ProbeResearch Required: Sectoid corpse (with slightly modified fluff on cybernetic interfaces).
Manufacture: 1 Sectoid corpse + 1 Elerium 115
Plasma Pistol/ClipResearch Required: Elerium 115 + Any live alien soldier.
Plasma Rifle/ClipResearch Required: Plasma Pistol + Live Snakeman or Muton soldier.
Heavy Plasma/ClipResearch Required: Plasma Rifle + Live Muton soldier.
UFO Power SourceResearch Required: Any live alien engineer + Elerium 115.
UFO NavigationResearch Required: Any live alien navigator.
Psi-AmpResearch Required: Psi-Lab + Ethereal Corpse
Manufacture: 1 Ethereal Corpse + 1 (or more?) Elerium 115
Flying SuitResearch Required: Alien Alloys, Power Source, UFO Navigation, Floater corpse or Cyberdisc corpse.
Hover-HWPsResearch Required: (Normal stuff) + Live Cyberdisc
Small LauncherResearch Required: Any live alien medic.
Hyper-wave Decoder (UFO Navigation research?)