The Weasleys, Ginny aside, are well written, as are the Longbottoms.
I remember going oooooooooh, when it was revealed that it could actually have been Neville who was the subject of Trelawney's prophecy.
It is a shame that JK felt impelled to churn out huge doorstops one after the other (presumably to satisfy a) the film companies and b) to keep up with her original (and clever, but ultimately unworkable) idea of following a generation of readers through high school with 7 books one after the other keeping in with her readers' ages. If she had taken more time, and realised that quality is to be prized over quantity, then I don't think there would be the gaping plot developments and poorly written characters.
The Chamber of Secrets- my absolute favourite, is a teeny book in comparison with the later ones, and it's perfect.
My Room 101 characters are: Ginny, Cho Chang, Tonks, Lily'n'James, Dumbledore and erm, Harry himself. But that has more to do with the plank of wood that goes by the name of Daniel Radcliffe. His Nimbus 2000 has more varied facial expressions than he does.