For the 10th annual QuakeCon event, QuakeCon 2005, the official QuakeCon website has the major highlights to be featured at the event mounted up. For those to lazy to click on the link, here they are:
Attend a keynote address by id Software co-founder and lead programmer John Carmack
Get a first look at QUAKE 4 multiplayer gameplay *
Get the latest details on Enemy Territory: QUAKE WARS
Go to two over-the-top, wild parties
Check out the $150,000 Nvidia Championships at QuakeCon
Meet Jon Farhat, visual effects supervisor, DOOM feature film
Attend the popular overclocking workshop sponsored by HardOCP
* Note the first look at Quake 4's multiplayer is bolded on the list, there's likely to be a demo of it finally shown at this years QuakeCon, with Capture the Flag, Deathmatch, Team Deathmatch, Last Man Standing, Tournament, and etc game modes. For the rest of the details, again, check out the official QuakeCon website.