Material gifts are not everything. You could spend time with your parents around the holidays (if they live close). Personally, I think sharing an experience with the people you love far exceeds anything you could buy in a store. Not only do you get to spend time with the people you care about, you will also have new memories that you can treasure forever.
For my mom's 50th birthday, I went horseback riding with her in the mountains. She still talks about it!
If your parents are too far away, you could buy a gift certificate to a restaurant, theatre, couple message, ski weekend-- or whatever else they are into.