Fever_Discordia: Still a couple of Sierra ones not mentioned - the Laura Bo games - The Colornal Bequest and... the other one!
Good call, I believe you mean The Colonel's Bequest and Laura Bow: The Dagger of Amon Ra.
While I haven't finished the second one, I would say that the Colonel's Bequest is very good (albeit old school, and text commands can sometimes take time to figure out), but it's one of the few games where the story develops independently in real time and you need your detective skills to measure up to the evolving situation.
Fahrenheit (Indigo Prophecy) would be another game to consider, though you play both from the perspective of detectives and the criminal.
Another one worth a look would be Bureau 13, where you can choose two different characters and your style of play depends on their talents. The sci-fi universe is based on an RPG and a series of books. I don't know where to find it now though.
I played through Jack Orlando - average at best in my opinion, you would definitely do better with the above and what others have already suggested (GK, PQ, Tex Murphy games etc.).