A lot of the better ones have been mentioned already. Sanitarium, most of the King's Quest games, most of the Space Quest games, and the Monkey Island games are great places to start if you want adventure games. I'm not sure why you specified "no RPGs", but if you're willing to waive that, the Quest For Glory games are also great adventures. (They're still adventure games with adventure game-style puzzles, just with stats and battles too.) I haven't gotten very far in Loom yet, so I can't judge it first-hand, but it's recommended often enough that you might want to give it a shot.
Also, check out the various adventure game sites and developers for more obscure gems and fan-made games.
AGD Interactive has done
fantastic remakes of the first two King's Quest games (I think they're better than the originals!), and you can find a lot of fan-made and abandonware offerings at sites like
The Underdogs.
Jam it back in, in the dark.
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Amanda