Love puzzle games so much, Syberia is on my list to play.
The old ones really are the greats, there's an entire series of Monkey Island to play through, Day of the Tentacle, Full Throttle, Sam and Max. More recently on the SCUMM engine I played Resonance which I thought was really quite good, the same studio made another couple like this which I've not played yet but are on my list to play The Shivah and The Blackwell Legacy.
Another good game I played recently was Deponia and bought the first sequel Chaos on Deponia, there's also a 3rd, the 2d art is really beautiful, reminds me of the higher resolution The Curse of Monkey Island when the graphics took a jump to more intricate yet still cartoony graphics.
The entire Broken sword series is really good, there was another one made recently which I finished not long ago and really enjoyed.
The entire Leisure Suit Larry series is really good, I think Love for sail was my fave, again had the right style of cartoon graphics but in a much higher resolution that previous SCUMM engine titles.
Pendulo studios also make some pretty good puzzle games among them the Runaway series (A Road Adventure, A Twist of Fate, The Dream of the Turtle) as well as couple of others one called Yesterday and another called The Next Big Thing - some of these have free demos on steam.
Also from memory there was a Discworld puzzle adventure game or 2 which I thought were really decent.
More recently I kickstarted Broken Age which is fairly good, has it's own weird style but I enjoyed it.
hmmm what else.
Going through my steam list I thought Still Life and Still Life 2 were both good murder mystery puzzle adventures.
I have Post Mortem still to play.
Oh and Machinarium is quite cute but a tough puzzle adventure game, one of the more difficult ones in recent memory, good for advanced players I'd say.
I personally found Dreamfall and The longest Journey a bit boring/frustrating :s
Oh god How can I forget Braid god damn, this is a really amazing puzzle game not so much adventure but has some of the best time based puzzles you can find.
That'll do for now xD