Lavender
Rose petals
Patchouli
Lemon verbena
Orris root (which has a violet scent of its own and is used as a fixative, and IMO indispensible in a potpourri)

Of course, there are many more options, and it depends on whether you want an 'old-fashioned' potpourri, or a 'spicy' potpourri - or a combination.

You can use cinnamon bark, scented-geranium leaves (there are many options here - rose, lemon, peppermint, nutmeg, apple, lime, coconut....), heliotrope, angelica root, sage (flowers or leaves), rosemary (flowers or leaves), thyme (lots of choices here too!), citrus peelings, cloves, calendula petals for colour. Pretty much any herb or spice which gives an aroma which is pleasant to your nose.

HINT: Put your bowl(s) of potpourri where passers-by will be tempted to touch them. It's when they are stirred around that they release their perfume. Encourage your guests to finger your potpourri. Or keep it near an open window, where the breeze will help to waft the perfume around.

And to keep your potpourri smelling nice over time, every now and then, add a drop or two of essential oil to it, and stir it in with the fingers. What about some ylang-ylang, or sandalwood, for instance?

Lavender
Roses
Patchouli
Lemon thyme
Rosemary

If you are talking spices or other plants, citrus peel, cinnamon, cloves, allspice, etc. A book worth looking for, published in 1986, is "The Scented Room" by Barbara Milo Ohrbach.

Lavender

Rose

Patchouli

Sandalwood - although like many prized woods there are sustainability issues and I generally avoid this one though I dearly love the earthiness of it

Any of the fragrant cooking spices - clove, allspice, cinnamon, nutmeg, vanilla, lemon peel, etc....

I must say I also like the pine and cedar fragrances as well but then I've always preferred the wood scents to the floral ones. Frankincense and myrrh make my list too of favorite natural scents.

FataMorgana

Not necessarily herbs, but:

Lavender
Fragrant rose petals (Midas Touch also dries to a vivid bright yellow)
Rose geranium leaves
Lemon verbena
Rosemary

Also artemisia, salvias, lemon-scented geranium leaves and lemongrass, bay laurel, dried butterfly ginger flowers, sage, tangerine peel....

Thank you for the suggestions and Herbalbetty, thank you for the book reference. It seems there are several favorites, some of which I had already planned to put in the garden :)

I know this shows I'm still a beginner with herbs, but what is Patchouli?

Lemon Verbena and Rosemary would be annuals here, but I'm thinking of trying them in pots for the summer. Is that better, or should they just be planted in with the perennial herbs?

Lass, patchouli is a tropical plant that has heavenly smelling leaves. It keeps its scent when dried. Definitely a plant very sensitive to frost.

Lemon verbena and rosemary are also either treated as annuals or houseplants here in zone 5. I've grown both in containers and also in the ground as an annual. Growing them in the ground will give you much more vigorous growth, but you have to dig them up to bring them in for the winter or treat as you would any other annual and say bye-bye in the fall. When I bring my potted lemon verbena inside for the season, after a week or two, it will shed all its leaves. If this happens to your plant, be patient. Within another week or two, new leaves will emerge. I have two potted rosemarys and they do well coming indoors for the winter. I keep them in a cool room of the house, in a south facing window. I've had them for 7-8 years. I have a lot of other tropicals which summer on the porch or deck and live in that cool room (60 degress) for the winter. Black pepper, vanilla orchid, Iboza, turmeric, cardamom, galangal, costus, Helichrysum, Vick's plant, He Shou Wu, Gotu Kola, Jiaogulan, etc.

There are zone 4 hardy roses and rose is a wonderful scent. The red-orange hips are a nice visual in a potpourri.

Pine, larch, cedar, etc. cones of various types are also a nice North Woods addition to a potpourri dish.

FataMorgana