Val's Crafting Meltdown corrects the recipe while also leaving the original in.

Craftable Water Arrows has become a must for thief types.

Midas Magic is fantastic. No matter what type of character you're playing the spells it has are awesome.

Phenderix Magic is also pretty cool. I've been watching a Let's Play with it, and it's got some awesome tricks.

Oh and Psijic Teleportation seems entertaining, but it's very obscure to try and actually FIND the spells. I still haven't. I've had to add them with the Console to play with them at all.