Here's how I would feel about various expressions of thanks, for something like writing a letter of recommendation:
No response at all: I might be a little disappointed but if I am busy I might not even notice. Some people might be more offended.
Email saying thank you: Feels perfectly sufficient to me.
Handwritten note: A very thoughtful gesture.
Token gift (small box of candy, desk trinket, etc): Appreciative but slightly embarrassed.
Gift of non-negligible monetary value: Quite embarrassed. I would probably gracefully try to decline it.
Gift of money, in any amount: Very uncomfortable. Feels like a bribe. I'd refuse.
Of course this could vary by culture (I'm in the US).
Regarding gifts for an advisor: A common tradition is to give your advisor a nicely bound copy of your dissertation, for their reference and as a memento. (Also be sure to thank them in the dissertation!) You could accompany it with a nice personal note. But again, I wouldn't suggest anything of significant value.