I know Yamaha were going to until 2010, but after that is un clear at the mo. I think the Japanese manufacturers are more likely to cease production as they like to be seen as 'politically correct' if you like.
The European manufacturers, KTM, Husqvarna, TM will more than likely continue to make 2 strokes (KTM & Husky have announced 2010 bikes and 2 strokes are in their range) as they are becoming more popular again and their bikes all comply with the emission standards.
Only time will tell...!