Al1: Jurassic Park Trespasser. Without a doubt the most professionally produced LP ever. Nothing else I have seen even comes close. It's also really informative, and good fun.
http://lparchive.org/LetsPlay/Trespasser/
Zjeraar: Thanks for that one!
Let me propose one of my own:
[url=]http://www.youtube.com/user/Atomaround[/url]
The guy plays most, if not all, games for the first time, so he doesn't necessarily have a lot of info on the game he's playing and you can forget about him scurrying through, but he's topical and has a good voice.
I enjoyed watching him go through parts of Machinarium.
The same guy who did the Trespasser LP also did a LP of Jurassic Park: Chaos Island, an RTS, and is currently doing an LP of Crimson Skies, although in the case of Trespasser and Crimson Skies, it would be more accurate to call them, as many have already done so, documentaries on the games.