Trip Hop Anthology (2006)
Thought of these while shuffling...
Classic compilations, essential to anyone's collection.
Aside from the Headz compilations these are probably the best compilations to give to someone unfamiliar with one of the defining music styles (as abused as the genre title is) of the 90s.
Trip Hop Anthology Vol. 2 (2010)
The second compilation which I didn't even know about until not too long ago.
Four discs of tracks will keep you lost in blissful reminisce for days.