Ok, Ive tried and I've tried but...HOW IN THE BLAZES DO YOU KILL THOSE ANNOYING WILL-O-THE-WHISP! Is it just me or are those things beyond annoying?

The key is to see them before they see you. Easier said than done, I know. I try to do a lot of damage, quick as possible. If you aren't good at delivering big damage in melee (or, more importantly, aren't good enough a sneak to catch them unawares so you can deliver said big damage) you'll need to snipe them with a good bow (poisoned arrows are helpful) or use a big spell. But really, the key is see and hurt them before they see you.

If you can't avoid a "fair" fight, best to carry some appropriate potions and a good fast blade. They can disappear in an instant (as you have no doubt noticed, judging from your frustration) so I think a fast weapon (a good dagger or shortsword) will probably make them easier to hit.

To elaborate on Canis' reply-

Wisps are immune to poisons and normal weapons. You need at least 2 of the following:

A powerful ranged attack- either enchanted (not poisoned) arrows and/or bow OR magical spell/scrolls (such as a fireball)

A powerful melee weapon with magical (fire, frost, or shock) damage.

A Detect Life spell, scroll, or item to see them when they "phase"

Potions to replenish whatever the Wisp drains (usually Health and Magicka)

Thanks for the help. I hate those damn things.

you have to have an enchanted item to kill them

Regardless of the forum I join, I seem to be the only one who hasn´t had any trouble with them! Not even when I was new to the game.
I usually let an elemental spell do the trick and I did that right off the bat, often in conjunction with an enchanted weapon which I always carried anyway.

So forgive me for smiling whenever I read about people having trouble killing them!

That is interesting. I knew of will o'the wisps from my tabletop days, so I already knew of their ability to go invisible and move very quickly. I'm pretty sure the first time I encountered one I was still completely freaked out, though. I don't remember the moment, but it probably was my screaming like the Angry Video Game Nerd. f**k!!! GOD-DAMMIT MOTHER f*****g S*** GET AWAY FROM ME YOU *****!!!

As treydog says, a character using Detect Life will be okay.

Buffy picks up their glow from hundreds of feet away - long before they can see her. Then she hits them with a combo spell that both immobilizes them and busts their poison immunity. She then immediately chases the spell with a poisoned arrow. Between the spell and range, the wisp has no idea where to seek the source of their pending death. When the glow extinguishes, Buffy moves on; one cannot recover arrows from wisps, and their glowing dust is hardly worth the long hike to track down their slippery green goo.

Ah, the beautiful language of nerds.

XD

Ranged kills if possible.
Try to get them when they are still, also Niamh always seems to end up with damaged luck...

Will-O-The-Wisps, *shudders* I never manage to kill them quickly. It always ends up with my character running for their lives, spamming detect life, and dodging that first attack when they become invisible before counter-attacking.

Give me trolls
Give me minotaurs
Give me daedra and zombies
Hell, give me Daedric Princes to fight
But please, please, PLEASE
Keep the Will-O-The-Wisps to yourself

WotWs were dangerous in the table games, too, for the exact same reasons they are dangerous in Elder Scrolls. I have a respect and an admiration for these creatures because of this (the way I have a respect and an admiration for a venomous snake here on Earth), the difference is that here on Earth I only see venomous snakes at the zoo, safely behind a glass display.

What are Will-Os anyway? I think they´re just swamp gas myself

I think Will-Os are a cereal brand made by Wil Wheaton...

Does that make those who successfully hunt them cereal killers?

Buffy uses plenty of range, detect life and weakness to poison to bust their immunity. They do set off alarms for her though, as she is quite cautious they do not get anywhere near her precious mare.

Somewhat off topic, but regarding the mare, in Skyrim, my battle cry is "Not the hooooooooooooooorse!"

I've shouted something similar playing Oblivion, when enemies ignore my character to go for the 4000 septim horse that's just standing there.

Oooooooh-hoo! No, you did not just say that!

Will-Os are no worse than rats if you ask me. Which you didn´t