I am 22, so hopefully can help you out here.
Jewelry- For my graduation this past May, my sister gave me a beautiful pair of Elsa Peretti earrings from Tiffany that I had wanted for a while. They are silver mesh diamond earrings with pearl studs and are timeless. Some classic piece of jewelry is always a good call. I also agree with the watch suggestion.. Michael Kors's watches are really popular with my age group if your daughter likes the trendy oversized watch look. If you want something more classic, I think Victorinox watches are great too.
Technology- My latest tech obsession is the new iPhone (since I do not have a smartphone yet), so maybe she would like something along those lines? A nice camera is always great too... or, as someone else mentioned, the iPad if you want to give her something really nice.
Travel- One of my favorite gifts is always anything travel related! My graduation gift from my mom was a 4-nt mother-daughter trip to WDW this December since we both have always wanted to visit during the holidays! Another idea is just offering to pay airfare for a future trip or taking her away for a long weekend somewhere local. Travel of any kind is always great.
Casino Night- I actually did this on my 21st birthday! My dad is a musician and was playing a gig at a local casino, so my parents just got my best friend and me a hotel room there for the night. It would be especially fun if she had a group of friends to go with for a full weekend or something.
Clothes- You can never go wrong. Same goes for shoes too... I am especially in love with boots this time of year!
You obviously know her best, but these are just some of the things I would enjoy. Congrats to your DD! Turning 21 was the best thing ever.
