You can stream them at starwars.com. There have been 10 episodes aired right now and there won't be a "new" episode until Jan 2.
The following is a part of this weeks issue of Star Wars Homing Beacon:
Although the final original episodes of Star Wars: The Clone Wars have aired for the remainder of 2008, there's no dearth of Clone Wars fun available at StarWars.com to keep fans busy until January 2nd, including the first-ever online "marathon," which begins on Monday.
Starting December 22, all 10 episodes of the hit Cartoon Network series that have aired to date will be available online at the official Star Wars website and at CartoonNetwork.com. What's more, each episode features a video commentary by supervising director Dave Filoni; a web comic; and a detailed episode guide containing concept art and additional insights into Star Wars: The Clone Wars. The online marathon ends on Monday, Jan. 5.
Kind of ironic that I saw your question right after I got done reading the latest edition of the Homing Beacon ... lol ...
A couple things to note ... first, you don't have to wait for the "marathon" to see all 10 episodes, you can go right to starwars.com and watch all 10 of them in a 5 hour period as each episode is 30 minutes. Second, when a new episode airs it is available to stream from starwars.com 2 days after it airs.
May The Force Be With You ...