Aside from crib bedding sets (which you can find many items for in my themed Baby Bedding Sets Page) your other key nursery decor items are going to be furnishings like lamps, rugs or throw pillows. With curtains I'd advise that you try and match the color of them up with the bedding which always looks very tasteful. Matching window valances are sometimes included with crib sets or can be bought as optional extras.
I love the super sweet Jungle Jill range of items which come in girly pinks. The 30 x 40 inch rug which features a giraffe, monkey and pink flowers would look perfect in a baby girl's bedroom. The lovely thing about the Jungle Jill range (aside from the gorgeous design) is that there are lots of matching items available to purchase as well. The cute cotton tales lamp which features this gentle animal, a zebra and a polka dot pastel green shade is ideal for a baby boy or girl. Pastel green works very well with pink for a girl's room or with a rich, chocolate brown for a boy's room.
Pillows always come in handy. I used pillows more for me when I had my daughter because of all the hours I spent gently rocking her to sleep. A really great tip is to keep a comfy chair for you, plumped up with pillows in your nursery. You need somewhere relaxing to sit (on your own and with your little one) because you could be spending hours in there if they are finding it hard to sleep and also just so you can watch over your precious little one in comfort.