Your professor may enjoy a gift of food, particularly if it is indulgent or something she wouldn't normally buy for herself. A small box of cheesecake bites or brownies from a bakery are a big hit, as they can also be shared with her family. Alternately, you could give your professor a fruit basket for a healthy treat. A special food from a recent vacation or study abroad trip is also a good gift.
Job-related gifts do not have to be boring or even useful. Many fun options for academic-related gifts are available. Choose a whimsical t-shirt that has a joke about your professor's field. For example, an English professor might enjoy a shirt with a saying such as "Of course I'm right; I'm an English teacher." Or, buy a variety of specialty items that will reflect your professor's field, such as coffee mugs, magnets, bumper stickers or even mouse pads.
Making something is a good way to offer an inexpensive gift to your professor, and homemade gifts are more meaningful and touching. A hand-knitted scarf or a small wooden box are perfect mementos of your time at the university, and will always remind your professor of you. If cooking is your talent, a cake or box of cookies says "thank you" just as well or better than anything purchased from a store.
A gift certificate to a book store, restaurant or coffee shop will always be appreciated. Your gift doesn't have to be expensive, even $5 or $10 is enough to express your gratitude. Gift certificates are available at many places, such as movie theaters, hardware stores, theme parks, department stores, cosmetic stores, spas and even sporting goods stores. With this variety of options, you can find something that your professor will enjoy.