Koge*2 House is the circle of Koge Donbo, who is currently very popular, being the main manga illustrator for Di Gi Charat. I'm pretty sure she's a high-end circle. ("High-end" means a circle or doujinshi that is made by an artist that is a popular professional artist, I think.) This is the only high-end circle I've bought stuff of to date, not because I don't love high-end art, but because most of the professionals make H doujinshi. :P But it was interesting enough that Koge Donbo had dipped into HP, so I sprang for it. There's also at least two doujins following the one below on the same theme, although both are smaller.

Title : Tension Living with Muscle 3 Published : 30/Dec/2001 Size : B5 Comments : I know, I know, the title is weird. Anyway, this book is very nice. It's obvious Koge is a pro, not just from the artwork, but the composition, proportion, etc. The stories are mostly about Harry and Ron, with Hermione, Draco, Colin and Percy all appearing a bit, and Ginny, Fred & George appearing just once each. Gorgeous illusts, funny 4-komas, and two nice guest arts. (Yes! It's confirmed! One is by Tohru Adumi! XD WAAaaaai!) It is mildly RonxHari, but you wouldn't know unless you read her comments. [68 pgs]

Koge*2 House's Harry Potter website: