daedra
scamps could be ordered to create distractions or steal important stuff (such as keys from behind a locked gate or a guards pocket. charging up would give a herne instead of a scamp at no extra magika (as the stronger herne is less stealthlike due to having hooves)
daedroths would terrify you enemy's more and act like a juggernaught .
winged twilights would fly, distracting enemies with hit and run tactics and chase dragons
dremora would fight like an average human but with more courage and health. they could use human things like levers, seige equipment and stuff. charging the spell up would give the possibility of a slightly higher rank
xivilai would be great at defence. they should be able to hold of many lesser enemies well whilst put on a narrow path such as a bridge or a corridor in a dungeon so long as they have enough room to swing their claymore .
clanfears would be very fast and agile and able to catch up to any opponent and jump over obstacles . they would not play defensive at all (think of an attack dog)
spider daedra would be aggressive and stealthy (and hopefully have a wallwalking ability) (think of the aliens from the "alien" movies)
dremora archer spell is needed
id like more daedra, but those are just the ones that stand out to me. you should be able to have conversations with them too.
undead
zombies would not be summoned from thin air- instead they should be created by using the "reanimate" spell on dead people.
skeletons should be created by using "reanimate" on a pile of bones. if different bones are used a different skeleton will be made.
ghosts, wraiths and banshees would be made by using a "summon spirit" spell in a certain areas. better ghosts come depending on the area, luck and skill.
there should only be three spells related to summoning undead (not including "turn undead")
lesser reanimate (zombies,smaller skeletons)
greater reanimate (more powerfull spirits inside people to make zombies and larger skeletons possibly including mammoths and dragons)
summon spirit (ghosts,wraiths,banshees- you could probably get a spirit inside of you to boost attributes- every kind of spectre except for nether liches )
and "dispell" should work against undead depending on the magnitude