Gift to a supportive professor? As you might have seen from my history I had a very bad advisor who deliberately underpaid me, stole my research work and undermined my career at multiple phases.

Now I am done with my university and leaving next month. A professor in my department had been very supportive of me during these times, giving me advice on how to handle this situation, gave me recommendation letters to apply for PhD programs at other universities and also got me a internship. I just want to thank her for her help. I usually would have got a champagne or something but I know she doesn't drink alcohol. Any advice?
It's nice that you want to do this for your professor. Thinking over what I would like (and have received in the past), the following comes to mind:


a note (email, letter, whatever you prefer) saying essentially a longer version of what you said above. A heartfelt note of this kind is the best kind of thanks. 
if you'd like to get something more tangible for the professor, a little token that they can place on their desk (like what Pete L. Clark mentions) is always nice. It doesn't even have to cost lots of money. I have students who made paper models for me (I teach geometry) and I have them all over my desk :).