The 'Conjuration – Reanimate' spells you can get improve as you level up your Conjuration Skill:
(Conjuration – Reanimate Spell, Conjuration skill level requirement, and the spell description)
Raise Zombie – 0 – Reanimate a weak dead body to fight for you for 60 seconds
Reanimate Corpse – 25 – Reanimate a more powerful dead body to fight for you for 60 seconds
Revenant – 50 – Reanimate a powerful dead body to fight for you for 60 seconds
Dread Zombie – 75 – Reanimate a very powerful dead body to fight for you for 60 seconds
Dead Thrall – 100 – Reanimate a dead body permanently to fight for you
Based on these descriptions, it is hard to know what exactly the spell will work on. What is a weak dead body? A more powerful dead body? A powerful dead body? etc.?
Skyrim classifies creatures and NPCs into generic classes as enumerated on the pages below:
List of Creatures (from UESP)
List of Generic NPCs (from UESP)
Within each of these classes, there is also a breakdown of more powerful types of those classes that are added as the player levels. So within the Bandit class, there is the initial Bandit, then the Bandit Outlaw, then the Bandit Thug, etc. From this information, it seems apparent that the weak, more powerful, and powerful descriptions may be related to the type within each creature or NPC class as the types themselves do not scale to the player's level with the exception of boss-types. The Reanimate spells' qualifications of power may relate to class as well.
From http://uesp.net/wiki/Skyrim:Leveling#Effects_of_Leveling :
…all leveled enemies are generated more like leveled creatures in Fallout. For example, Bandit NPCs are always a fixed level for their name (Bandits are level 1, Bandit Thugs are level 9, Bandit Highwaymen are level 14, etc). The player's level affects the range of possible bandit types generated within a bandit dungeon, and probably the frequency, but does not seem to affect the resulting stats except in a few rare cases. Lower variant bandits remain reasonably common even when more dangerous bandits are available.
To optimize magicka consumption, it would be useful to know the minimum level of reanimation spell necessary for a given class and type of enemy. So, what is the minimum level of reanimation spell needed for each type of each creature and NPC class? It would be nice if there were a set of general rules such as "regardless of class of creature or NPC, if they appear after the player is between levels X and Y, then you need at least the level Z conjuration spell" or "these classes of NPCs and creatures all need at least the level Z conjuration spell."
Best Answer
Time for more Skyrim Science!
So while I don't have a full answer to your question just yet, I do have some preliminary results.
I've been peeking around in the Skyrim Creation kit, looking at the spell effects for the five spells you list above. For instance:
The highest level reanimate spell has a magnitude of 40.
This is similar to how the master level frenzy spell, Mayhem, is set up, though it's magnitude is 25. This becomes relevant as soon as we read the effect's description:
We've documented the frenzy effect over here already, so I think we can safely assume that if Reanimate works similarly (and there's no real reason it shouldn't), the magnitude of the spell effect correlates precisely with the maximum level corpse that can be raised.
That gives us this list:
Which gives us an obvious series for our curve.
Double-casting conjuration spells increases the duration, not the effect, so that won't help against higher level enemies, but the Necromage perk will.
As to what level are which creatures, the first thing to realize is that certain creatures (i.e., Dragons, Giants, and Dwemer Automatons) simply cannot be reanimated.
That said here's as good a list as I can manage. If you don't see an NPC on here, it's most likely because they can be found at multiple levels. Creatures are listed under the minimum required spell to reanimate them:
Raise Zombie (up to 6):
Reanimate Corpse (up to 13):
Revenant (up to 21):
Dread Zombie (up to 30):
Dead Thrall (up to 40):
Too Powerful to Raise