Author and knitter Alison Hansel wrote Charmed Knits: Projects For Fans Of Harry Potter in 2007. The book contains 28 magical patterns that are sure to delight Potterheads. Many of the patterns in this book can be found for free if you look hard enough, but this book conveniently puts them all in one place that you can refer back to any time you want.
Ms. Hansel clearly explains exactly what you need for each pattern, instructions with pictures, descriptions of the various knitting techniques, and definitions of the abbreviations used in the book. We Muggles might not be able to knit with magic like Mrs. Weasley but these patterns will make it look like we did!
Here is a list of the patterns found inside this book:
Weasley Knits
The Weasley SweaterDiagon Alley
Mrs. Weasley's Bag of Stitch Witchery
Molly's Amazing Technicolor Coat
Errol
Clock Blanket
Student Wizard Cap
Wizard Robe
Invisibility Shawl
Wand Cozies
Quidditch Sweater
Quidditch Socks
House Colors
House Scarves
House Hats
House Mittens
House Socks
House Sweater
Hip House Scarf
House Bookscarves
The Magic of Giving
Dobby's Socks
Elf Hats
Hermione's Magic Knitting Bag
Harry Christmas Ornaments
Phoenix Tears Scarf
Home at Hogwarts
Harry's Red Cable Sweater
Hermione's Cable and Bobble Hat
Hermione's Cable and Bobble Mittens
Ron's Animal Crackers Hat
Ron's Ragg Raglan
Here are a couple of pictures of two patterns in this book. The patterns are for the 'H' sweater Mrs. Weasley knit for Harry Potter during his first Christmas at Hogwarts. The second patter is for Mrs. Weasley's colorful sweater (she might not be a fashion plate, but she is nothing if not unique!).
I don't knit so I have no idea if these are laid out well or not, but I'm sure you will be able to tell if you are a knitter.