Google recently launched their XSS game. I haven't look yet, but I can bet there is at least a hundred guides/howtos online. They're always fun to read; tho, I often wonder what the person goes through to find each vuln.
That said, I have an unedited (other than adding audio to the silent video) video of me going through it. Mistakes and all.
Yes, I fully understand that some of my attempts were stupid, but I was trying to finish it fast.
Anyways -- enjoy and leave me comments as to what you thought!