I'm doing a vintage theme (because we live in a 140 year old house...), but I plan on making most of the decor myself. Boy or girl, I want white eyelet lace curtains and crib ruffle.
There isn't much bedding that you're supposed to use anymore--it sounds like the only thing recommended is crib sheets? The walls are dark green wall paper with peach flowers, so for a boy I'd do mint green sheets, and for a girl peach sheets.
I also plan on a quilted wall hanging using a simple traditional block, in whichever color scheme is appropriate. Although I'm also really liking some of the "classic" Winnie the Pooh items I see on Amazon, and I think those are really neutral so I may use some.