Black Hands Dagger
Item Quality: 9
Comment - for some reason a lot of people think this is the best weapon in the game. Personally I do agree that the BHD is a good dagger, but I do not think it is comparable to a really good sword... Besides, once you waste all the charges you need to wait weeks in game before the dagger is recharged. Using soulgems requires up to 20 (!?) Golden Saints to recharge fully.
Location - finish all the 'special' quests for the Morag Tong under the Arena in Vivec.
Fang of Hayneckhtnamer
Item Quality: 8
Comment - a very nice dagger, as you can see for yourself. Actually it's the most expensive dagger there is.
Location - Mamaea, Shrine of the Pitted Dreams.
Dagger of Symmachus (Tribunal Only)
Item Quality: 9
Comment - a very cool dager that is one of the most powerful Tribunal artifacts. It's so good you can give it to the museum (though I hate doing that ;-)).
Location - do the quests for the king.
The Keening
Item Quality: 10
Comment - There's nothing to say really.
Location - do the Morrowind main quest. You can find it in the Odrosal.
Saint's Black Sword
Item Quality: 6
Comment - nothing really special, just a relatively expensive dagger.
Location - Vivec, Telvanni Vault or in pocession of Minedhel in Dagon Fel, Sorkvild's Tower.
Soul Drinker
Item Quality: 8
Comment - a nice dagger, useful for capturing souls. However, since it casts soultrap every time you hit the enemy, it can be really annoying.
Location - do some Mage Guild quests and at one point you will be given this dagger.