The free open-source SCUMM implementation. Read more about it over at the utils section. This is the place to go for the latest updates and information on ScummVM.
LEC Quick & Easy
Having problems getting the old SCUMM games to run under newer versions of Windows? Then is this the place for you. They provide various tools that will help you out in your quest.
The Game File Formats Site
Features file format specifications to various games, including some for LucasArts' adventure games.
The LucasArts Museum
Screenshots, box art and pictures of anything realted to LucasArts' adventure games.
The International House of Mojo
Probably the best and most up-to-date LucasArts fansite. Features (almost) daily news, and hosts many different LucasArts-related sites, including this one.
AGI Development Site
Find loads of information on one of the first adventure game suthoring systems here - Sierra's Adventure Game Interpreter (AGI). Includes the program AGI Studio which you can use to create your own or edit existing AGI games. On the site you will also find homemade AGI games, articles and other interesting stuff dealing with AGI.
Sierra Creative Interpreter (SCI) is the adventure game authoring tool Sierra used for the their later adventure games. SCI Studio is still under development but it aims to be the SCI equivalent to the above mentioned AGI Studio.
AGI & SCI Message Board
It's the main AGI & SCI message board.
Adventure Game Studio
If you're interested in creating your own adventure games in the spirit of LucasArts' or Sierra's old games, then you should check out Adventure Game Studio which is one of the most popular adventure game authoring systems out there.
LucasArts official homepage, featuring a company store (for US residents only) where you can buy
many some of their classic adventure games.