Question: The two I can think of at the moment are Q and Nomad. Q's power is pretty much unlimited, and Nomad restored Scotty's life.

I guess maybe you could argue that Seven of Nine, or any Borg Drone, can also restore life, as Seven brought back Neelix from the dead.

Perhaps you could also include the Guardian of Forever or the Krenim as indirect restorers of life.

Answer: 
Looking at a [list of resuscitations](https://memory-alpha.fandom.com/wiki/Death), we have a reasonable idea:

* Augments: in *Star Trek Into Darkness*, Khan's blood is used to bring Kirk back from the dead from radiation poisoning
* Nomad: resurrected Scotty in *TOS* 'The Changeling
* The caretaker of the planet in 'Shore Leave': McCoy was killed by a Knight's Lance, but then revived
* The Genesis Device: revived Spock's dead body in *Wrath of Khan*/*Search for Spock*
* Skilled Starfleet Doctors: on a number of cases, we see that a being that is dead for a short enough period can be revived using Starfleet medical technology (e.g. Crusher in *TNG* 'Code of Honour' revived the dead Yareena)
* The Kobali (*VOY* 'Ashes to Ashes')
* Species 149 (whose reanimation technology was used by the Borg to reanimate Neelix in *VOY* 'Mortal Coil)

It is never demonstrated that Q have this power, although the events of *TNG* 'Tapestry' and 'Hide and Q', it is reasonable to conclude that they too have this power.
Charlie x's alien adopters brought back the people he made "go away"...