The longest continuing hacker gathering that we're aware of has announced the schedule for its talks later this month.
The 21st annual Chaos Communication Congress will be held in Berlin from December 27-29. (The gathering takes place on the same date each year.) The schedule so far can be found here. Topics range from new technology to activism to cryptography. In addition there will be a lockpicking seminar and competition plus films and a huge network area.
As this is taking place in Germany, the German language is extremely popular. However a good portion of the conference will be presented in English for the benefit of participants from other countries. If this is your first time visiting this country, you will have no problem communicating if you only speak English.
The Congress takes place at the Berliner Congress Center at Alexanderplatz in Berlin-Mitte. Tickets for all three days range from €25 to €40. Single day passes are also available.
A popular hotel of choice which is within crawling distance of the conference is the Park Inn Hotel. Cheap hostels also abound in the area.
The Chaos Communication Congress Wiki can be found at http://www.ccc.de/congress/2004/wiki.en.html.