Spellswords, Nightblades, Battlemages, Healers:

Spells can often get you at range and they're pretty handy in melee. At lower levels (up to about 4th) they simply try to melee with you. At mid-levels (4th to 7th or thereabouts), their spells tend to be non-lethal ones like "Silence". At higher levels they'll try to nuke you or paralyze you and then close for melee. Battlemages and Healers prefer ranged spells and can get off a couple before they close. Spellswords and Nightblades like to leech your magica, shock you and paralyze you and prefer spells with a range of "Touch". "Spell Reflection" can take care of a lot of this. Missiles are a good defense since you're probably a better archer than they are. Treasure usually consists of a couple of armor pieces, a weapon or two, money and potion ingredients.

Sorcerers:

Sorcerers are pussycats as long as you don't throw spells at them. Since they can't regenerate magica, they have to absorb it. As long as they don't have any they'll engage in missile fire or melee and they don't have many hit points. Bethesda could have made these guys tougher by giving them some magica to start with.

Mages:

Surprisingly enough, Mages like to get off a spell or two and close for melee. Maybe they think they're Warriors. Anyway, they can't stand toe-to-toe with anyone for very long, but their spells can put a severe hurt on you. Treasure is usually money, a weapon, and lots of potion ingredients.

Orcs

Orcs come in four types:

Orc

(Armor 7, Health 13 to 34, Damage 1-6):

A straight slugger, but the stated damage range is way on the low side (it's closer to 15 points at the top end – probably due to extra damage from high Strength). Treasure is usually less than 100 GP's, a few cheesy weapons and armor pieces.

Orc Sergeant

(Armor 5, Health 15 to 50, Damage 5-15):

Another straight slugger. Damage is a bit more severe than a regular Orc, but the chances of getting a decent weapon or armor piece are slightly better.

Orc Warlord

(Armor 0, Health 18 to 90, Damage 5-50):

The heavy hitter of the Orc family. He doesn't hit quickly, but he does hit hard. You usually won't encounter him at lower levels (except for a few pre-placed ones). There's a good chance of getting a decent weapon or armor piece off of him and he's usually toting a couple of hundred GP's.

Orc Shaman

(Armor 7, Health 18 to 74, Damage 2-20 + Spell [commonly Wizard's Fire and/or Invisibility]):

The Orc Shaman's favorite tactic is to blast you with a fire-based spell (at mid- to high levels), then turn invisible and try to beat you to death. It isn't unusual for them to be blown up by their own spells. If he turns invisible, just start swinging in that general direction and he'll walk right into it (no one ever claimed that Orcs were terribly bright). Treasure is commonly a few GP's, a couple of weapons and/or armor pieces and a few ingredients.

Centaurs

Centaur

(Armor 6, Health 14 to 42, Damage 5-15)

Their "Ho-ho!" is almost as annoying as "Halt! Halt! Halt!". Melee is their strong suit and they have enough hit points to stand for a few rounds. Treasure is usually money and weapons with an armor piece or two thrown in for spice.

Spriggans

Spriggan

(Armor -4, Health 12 to 26, Damage 1-8/1-8/1-10)

Walking trees. Tough hides (bark?) and lots of hit points. No missles from these guys. They like to slug it out and aren't very good at it. Treasure is potion ingredients and sometimes a few gold pieces. Supposedly they regenerate two or three times and come back at you, but I've never seen it.

Giants and Harpies

Giant

(Armor 3, Health 18 to 74, Damage 10-30)

Slow, big, ugly. But they hit HARD. Engage them with missiles or ranged spells if you don’t have many health points. Treasure is money and weapons with an occasional armor piece and/or ingredient.

Harpy

(Armor 2, Health 16 to 58, Damage 2-12/2-12/5-15 + Disease)

Flying uglies. They can inflict serious damage if you're not prepared and they also carry diseases (standard 0.5% chance of catching one). You need Dwarven or better weapons to hit. Treasure is usually a few GP and a couple of ingredients (like the Imp), but occasionally you'll come across a weapon or armor piece.

Nymphs

Nymph

(Armor 0, Health 15 to 50, Damage 1-5)

Naked girls. They don't damage your health; they drain your fatigue points. They don't have many hit points and aren't very good at melee. They can be encountered underwater. Treasure is usually a little money and a couple of ingredients.

Lamia and Dreugh:

Lamia

(Armor 6, Health 16 to 58, Damage 5-15 + damage fatigue)

Dreugh

(Armor 6, Health 13 to 34, Damage 5-15)

Always encountered underwater. Dreugh can sometimes be tough to hit because they're usually above you. No missiles or magic from these two; straight sluggers. Like the Nymph, the Lamia drains your fatigue points with each hit. Treasure for both is money and ingredients and an occasional weapon or armor piece.

Undead

Undead come in a variety of types. From the essentially annoying (Skeletal Wariors) to the truly deadly (Vampire Ancients and Ancient Liches). They can be encountered above ground, below ground and under water.

Skeletal Warrior

(Armor 2, Health 17 to 66, Damage 5-15)

They hit slowly and do not have a missile or magic attack. They're also very light. If you can position yourself just right you can hit them from the front and inflict damage when they slam the wall. In theory, edged weapons only do half damage. Once you've got a few levels they're strictly an annoyance. Treasure is a few coins, weapons and armor.

Zombie

(Armor 0, Health 52 to 66, Damage 15-50 + Disease)

They hit very slowly, but they hit hard. They've also got a lot of hit points. Don't try to stand toe-to-toe with them at lower levels. Either I've been very lucky or the disease part is wrong, but don't be surprised if it happens. Treasure is money and a couple of armor/weapons.

Wraith

(Armor 0, Health 20 to 90, Damage 20-45 + Spell [lightning, usually])

A spell attack followed by melee. Wraiths like to throw little fuzz-balls at you if you're far enough away. I haven't noticed any effect from them hitting and they never seem to reflect or absorb. In theory these are lightning balls, but if so, they don't work very well.

Ghost

(Armor 0, Health 17 to 66, Damage 10-35 + Spell [Wizard Rend])

A spell attack followed by melee. Ghosts like "Wizard Rend", but they will only hit you with it once. If there is a "Wizard Rend" effect already active on you, they will not throw others, but will close for melee instead. Since "Wizard Rend" has a range of "Touch", hitting Ghosts with missiles is a good defense. "Spell Reflection" also works very well.

You'll get to know Wraiths and Ghosts very well if you spend much time in Daggerfall between 7 pm and 5 am. You need Silver or better weapons to hit them. They move quickly, but hit slowly. They have a real problem with corners. If you can get them where they need to go around a corner to get to you, it's best to use missiles or run up and hit them a couple of times and then back off a few steps and do it again. Both are very difficult to see in dim conditions or after dark. Wraiths have dancing spots in them, but ghosts just have the red eyes. At night they'll turn kind of purple if you can get a light behind them. Treasure is an iffy proposition (most of the time they don't have any). When they do, it's usually one item: money, armor, weapon or ingredient. I have picked up the occasional magic item from them, though. You can pick their pockets (go figure).

Mummy

(Armor 2, Health 17 to 66, Damage 5-15 + Disease)

Hits pretty decently (I think the damage range given by Bethesda is a little on the low side) and the possibility of disease can be a major pain. Decent treasure if you like money and the occasional ingredient.