I was just wondering if there were mulitple sigil stones (maybe for sale or in dungeons) that you can use for the atronach forge. I really want some daedric armor but dont want to spend a bunch of points on smithing.

From http://elderscrolls.wikia.com: You can recieve a second Sigil Stone. If you place the stone in the Atronach Forge right after initially recieving it and then talking to Phinis. He will take nothing out of your inventory but return another Sigil Stone when completing the quest. The second Sigil Stone is effectively useless though.

It actually takes more stuff to create daedric armor at the atronach forge. If you really want some daedric armor you're easiest path is to get your smithing perks up.

And as far as I know you can not make a full suit of daedric armor (edit: at the atronach forge), only the torso. To make it you need the Sigil Stone, 1 Daedra Heart ,1 Unenchanted Ebony Armor, 1 Centurion Dynamo Core, 1 Black Soul Gem.

If you get your smithing level up to daedric then all you need are daedra hearts and making a whole suit of daedric armor is fairly easy.

What does the atronach forge do? It's better to craft items there?

You can create staffs for summoning, as well as summon spell tomes, and if you have a Sigil Stones, create Daedric stuff.

Is the Daedric better then smithing it at a regular forge?

It's the same.

Also i heard that you can create the Daedric pieces and retain the items you need aswell...