Hermione's Dress for Slughorn's Christmas Party

The dress was handmade by Jenny Packham thanks to Aerie_123
Here is a video where Emma talks about Hermione's wardrobe and the party dress

It is very similar to this dress:
http://www3.jcpenney.com/jcp/X6.aspx?DeptID=50434&CatID=56292&GrpTyp=PRD&ItemID=1727b47&attrtype=&attrvalue=&CMID=50434|50444&Fltr=&Srt=&QL=F&IND=10&cmVirtualCat=&CmCatId=50434|50444|56292

Taking apart Hermione's Bedroom from the Deathly Hallows

Coming Soon

Hermione Deathly Hallows Bill and Fleur's Wedding

This dress is designed by Jenny Packham
Some alternatives:
http://www.overstock.com/Clothing-Shoes/Connected-Apparel-Womens-Garnet-Scoop-neck-Dress/4287530/product.html

Shoes:
http://www.amazon.com/dp/B002R8Q97G/ref=asc_df_B002R8Q97G1039377?tag=the004-20&creative=380333&creativeASIN=B002R8Q97G&linkCode=asn

She is also wearing a pretty necklace. I haven't found it yet but I'm sure you can get jewelery makers on Etsy to make you one.