Um, I guess some spoilers are in these suggestions; specifically spoilers relating to the Forerunner Trilogy of books.
Planets:
The only suggestion I have here is that some sort of "dead" or "useless" world should be a "Glassed Planet" or "Glassed World." If possible, the option for the UNSC to colonize Glassed Worlds (after a lot of research of course) would be both flavorful and unique to the faction.
Artifacts:
"Resilient Metaloids" -> "Huragok Population"
Resilient Metaloids increases hull repair rate, which is exactly what you'd expect a bunch of Engineers to be able to help to do. Additionally, this works well for all factions since it represents finding a group of Huragok living in isolation on a planet, and then eventually being discovered by the faction and being put to work. The Covies obviously used them, and then the UNSC gets some later on as well.
"Data Archive" -> "Ancilla Data Fragment"
Ancilla, being Forerunner AI, were extremely intelligent and fully sentient. Finding even a fragment of an operating Ancilla would very easily boost that faction's ability to conduct research, or minimize cost for research, due to the Ancilla's experience and wisdom, and overall knowledge.
"Jump Drive Relic" -> "Slipspace Portal Generator"
Basically to play off of the Artifact in Voi. It's difficult to truly decide where to put this in the artifacts; frankly the Forerunners had ground-based portal projectors (the Voi Artifact), space-based ones, etc. I feel it would work best here, for star-to-star movement, since the portals that we have seen specifically are able to send ships to EXTREME distances in a VERY short time. I mean; the Artifact sent ships beyond the galactic rim. In less than a month (they left Nov 17, and arrived at the Ark Dec 11).
"Phase Accelerator" -> "Unbending Filament Remnant"
Somehow this survived the firing of the Halos. No reason to get into specifics as to why. The Precursor's technology which allowed them to connect worlds and systems across vast reaches of space. This would be used for the "planet-to-planet" travel for that reason.
"Kinetic Intensifier" -> "Ballistic Hard Light"
We all know what hard light is. Now imagine surrounding a plasma shot or missile with a sort of hard light sabot which increases the power of the weapon.
"Relativistic Factories" -> "Ancient Design Seed"
These were constructs of hard light used by the Forerunners to construct ships. Imagine finding one or more still intact; it could vastly increase ship construction.
