I always think of outdoor stuff when I think of "loose parts". Loose parts, to me, are any open-ended materials that can be defined by the children in their play. Loose parts in our outdoor environment include plywood, tubing, tires, sticks, stones, pine cones, bottles and buckets, ropes, scrap wood, pool noodles.
Indoors, we try to include some loose parts as well. Luminaries, dried oranges, pine cones, sticks, rocks, scarves. Luminaries might be my most favorite-ist indoor material. Candle light brings a sense of calm and serenity and centeredness. I've used real candles at circle time before (for holidays, birthdays, and just because).
Here are some other loose parts in the classroom:
dried oranges in baskets
silicon muffin cups
felted stones, felt shapes, and empty drawers from jewelry boxes (all on a home-dyed scarf)
We have an entire shelf of natural items for use by the children: pine cones and pine cone animals, felted stones, gourds, dried magnolia buds, dried oranges, felted people and shapes, sticks, and rocks. For a couple of weeks after setting up this shelf, I thought it was sort of a waste of space because the materials on it literally went untouched. However, one day, seemingly all of the children discovered how to use these completely open-ended materials in their play, and from that day forward, these items have been a staple in the children's dramatic play.